diff --git a/app/DataMapper/CompanySettings.php b/app/DataMapper/CompanySettings.php
index 3079a50988c3..d2241f95b2f5 100644
--- a/app/DataMapper/CompanySettings.php
+++ b/app/DataMapper/CompanySettings.php
@@ -495,7 +495,10 @@ class CompanySettings extends BaseSettings
 
     public $show_pdfhtml_on_mobile = true;
 
+    public $use_unapplied_payment = 'off'; //always, option, off //@implemented
+
     public static $casts = [
+        'use_unapplied_payment'              => 'string',
         'show_pdfhtml_on_mobile'             => 'bool',
         'payment_email_all_contacts'         => 'bool',
         'statement_design_id'                => 'string',
diff --git a/app/Services/Invoice/AutoBillInvoice.php b/app/Services/Invoice/AutoBillInvoice.php
index 73eac355eefe..549efee15b1d 100644
--- a/app/Services/Invoice/AutoBillInvoice.php
+++ b/app/Services/Invoice/AutoBillInvoice.php
@@ -22,6 +22,8 @@ use App\Models\Invoice;
 use App\Models\Payment;
 use App\Models\PaymentHash;
 use App\Models\PaymentType;
+use App\Repositories\CreditRepository;
+use App\Repositories\PaymentRepository;
 use App\Services\AbstractService;
 use App\Utils\Ninja;
 use Illuminate\Support\Str;
@@ -31,7 +33,7 @@ class AutoBillInvoice extends AbstractService
     private Client $client;
 
     private array $used_credit = [];
-
+    
     /*Specific variable for partial payments */
     private bool $is_partial_amount = false;
 
@@ -66,6 +68,12 @@ class AutoBillInvoice extends AbstractService
             $this->applyCreditPayment();
         }
 
+        nlog($this->client->getSetting('use_unapplied_payment'));
+        if($this->client->getSetting('use_unapplied_payment') != 'off') {
+            nlog("meeeeeeerp");
+            $this->applyUnappliedPayment();
+        }
+
         //If this returns true, it means a partial invoice amount was paid as a credit and there is no further balance payable
         if ($this->is_partial_amount && $this->invoice->partial == 0) {
             return;
@@ -176,9 +184,6 @@ class AutoBillInvoice extends AbstractService
 
         $payment->amount = 0;
         $payment->applied = 0;
-
-        // $payment->amount = $amount;
-        // $payment->applied = $amount;
         $payment->client_id = $this->invoice->client_id;
         $payment->currency_id = $this->invoice->client->getSetting('currency_id');
         $payment->date = now()->addSeconds($this->invoice->company->utc_offset())->format('Y-m-d');
@@ -217,8 +222,6 @@ class AutoBillInvoice extends AbstractService
              ->client
              ->service()
              ->updateBalanceAndPaidToDate($amount * -1, $amount)
-              // ->updateBalance($amount * -1)
-              // ->updatePaidToDate($amount)
              ->adjustCreditBalance($amount * -1)
              ->save();
 
@@ -243,6 +246,79 @@ class AutoBillInvoice extends AbstractService
                     ->setCalculatedStatus()
                     ->save();
     }
+    
+    /**
+     * If the client has unapplied payments on file
+     * we will use these prior to charging a 
+     * payment method on file.
+     *
+     * This needs to be wrapped in a transaction.
+     *
+     * @return self
+     */
+    private function applyUnappliedPayment(): self
+    {
+        $unapplied_payments = Payment::query()
+                                  ->where('client_id', $this->client->id)
+                                  ->where('status_id', Payment::STATUS_COMPLETED)
+                                  ->where('is_deleted', false)
+                                  ->where('amount', '>', 'applied')
+                                  ->where('amount', '>', 0)
+                                  ->orderBy('created_at')
+                                  ->get();
+        
+        $available_unapplied_balance = $unapplied_payments->sum('amount') - $unapplied_payments->sum('applied');
+        
+        nlog("available unapplied balance = {$available_unapplied_balance}");
+        
+        if ((int) $available_unapplied_balance == 0) {
+            return $this;
+        }
+
+        if ($this->invoice->partial > 0) {
+            $this->is_partial_amount = true;
+        }
+
+        $payment_repo = new PaymentRepository(new CreditRepository());
+        
+        foreach ($unapplied_payments as $key => $payment) {
+            $payment_balance = $payment->amount - $payment->applied;
+
+            if ($this->is_partial_amount) {
+                //more than needed
+                if ($payment_balance > $this->invoice->partial) {
+                    $payload = ['client_id' => $this->invoice->client_id, 'invoices' => [['invoice_id' => $this->invoice->id,'amount' => $this->invoice->partial]]];
+                    $payment_repo->save($payload, $payment);
+                    break;
+                } else {
+                    $payload = ['client_id' => $this->invoice->client_id, 'invoices' => [['invoice_id' => $this->invoice->id,'amount' => $payment_balance]]];
+                    $payment_repo->save($payload, $payment);
+                }
+            } else {
+                //more than needed
+                if ($payment_balance > $this->invoice->balance) {
+                    
+                    $payload = ['client_id' => $this->invoice->client_id, 'invoices' => [['invoice_id' => $this->invoice->id,'amount' => $this->invoice->balance]]];
+                    $payment_repo->save($payload, $payment);
+
+                    break;
+                } else {
+                    
+                    $payload = ['client_id' => $this->invoice->client_id, 'invoices' => [['invoice_id' => $this->invoice->id,'amount' => $payment_balance]]];
+                    $payment_repo->save($payload, $payment);
+
+                }
+            }
+
+            $this->invoice = $this->invoice->fresh();
+
+            if((int)$this->invoice->balance == 0) {
+                return $this;
+            }
+        }
+
+        return $this;
+    }
 
     /**
      * Applies credits to a payment prior to push
@@ -260,7 +336,7 @@ class AutoBillInvoice extends AbstractService
 
         $available_credit_balance = $available_credits->sum('balance');
 
-        info("available credit balance = {$available_credit_balance}");
+        nlog("available credit balance = {$available_credit_balance}");
 
         if ((int) $available_credit_balance == 0) {
             return $this;
@@ -332,14 +408,6 @@ class AutoBillInvoice extends AbstractService
                                 })->orderBy('is_default', 'DESC')
                                 ->get();
 
-        // $gateway_tokens = $this->client
-        //                        ->gateway_tokens()
-        //                        ->whereHas('gateway', function ($query) {
-        //                            $query->where('is_deleted', 0)
-        //                                   ->where('deleted_at', null);
-        //                        })->orderBy('is_default', 'DESC')
-        //                        ->get();
-
         $filtered_gateways = $gateway_tokens->filter(function ($gateway_token) use ($amount) {
             $company_gateway = $gateway_token->gateway;
 
diff --git a/tests/Feature/Payments/AutoUnappliedPaymentTest.php b/tests/Feature/Payments/AutoUnappliedPaymentTest.php
new file mode 100644
index 000000000000..96e3a967a22f
--- /dev/null
+++ b/tests/Feature/Payments/AutoUnappliedPaymentTest.php
@@ -0,0 +1,180 @@
+<?php
+/**
+ * Invoice Ninja (https://invoiceninja.com).
+ *
+ * @link https://github.com/invoiceninja/invoiceninja source repository
+ *
+ * @copyright Copyright (c) 2021. Invoice Ninja LLC (https://invoiceninja.com)
+ *
+ * @license https://www.elastic.co/licensing/elastic-license
+ */
+
+namespace Tests\Feature\Payments;
+
+use App\DataMapper\ClientSettings;
+use App\Factory\InvoiceFactory;
+use App\Helpers\Invoice\InvoiceSum;
+use App\Models\Client;
+use App\Models\Credit;
+use App\Models\Invoice;
+use App\Models\Payment;
+use App\Utils\Traits\MakesHash;
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Foundation\Testing\DatabaseTransactions;
+use Illuminate\Routing\Middleware\ThrottleRequests;
+use Illuminate\Support\Facades\Session;
+use Illuminate\Validation\ValidationException;
+use Tests\MockUnitData;
+use Tests\TestCase;
+
+/**
+ * @test
+ */
+class AutoUnappliedPaymentTest extends TestCase
+{
+    use MakesHash;
+    use DatabaseTransactions;
+    use MockUnitData;
+
+    protected function setUp() :void
+    {
+        parent::setUp();
+
+        Session::start();
+
+        $this->faker = \Faker\Factory::create();
+
+        Model::reguard();
+
+        $this->makeTestData();
+        // $this->withoutExceptionHandling();
+
+        $this->withoutMiddleware(
+            ThrottleRequests::class
+        );
+    }
+
+    public function testUnappliedPaymentsAreEnabled()
+    {
+        
+        $settings = ClientSettings::defaults();
+        $settings->use_unapplied_payment = 'always';
+
+        $client = Client::factory()->create([
+            'company_id' => $this->company->id,
+            'user_id' => $this->user->id,
+            'settings' => $settings,
+        ]);
+
+        $this->assertEquals('always', $client->settings->use_unapplied_payment);
+
+        $invoice = Invoice::factory()->for($client)->create([
+            'company_id' => $this->company->id,
+            'user_id' => $this->user->id,
+            'auto_bill_enabled' => true,
+            'client_id' => $client->id,
+        ]);
+
+        $invoice  = $invoice->calc()->getInvoice();
+
+        $payment = Payment::factory()->for($client)->create([
+            'company_id' => $this->company->id,
+            'user_id' => $this->user->id,
+            'client_id' => $client->id,
+            'amount' => 100,
+            'applied' => 0, 
+            'refunded' => 0,
+            'status_id' => Payment::STATUS_COMPLETED,
+            'is_deleted' => 0,
+        ]);
+
+        $invoice->service()->markSent()->save();
+
+        $this->assertGreaterThan(0, $invoice->balance);
+
+        nlog($invoice->balance);
+
+        try{
+            $invoice->service()->autoBill()->save();
+        }
+        catch(\Exception $e){
+
+        }
+
+        $invoice = $invoice->fresh();
+        $payment = $payment->fresh();
+
+        nlog($invoice->toArray());
+        nlog($payment->toArray());
+
+        $this->assertEquals($payment->applied, $invoice->paid_to_date);
+        $this->assertGreaterThan(2, $invoice->status_id);
+        $this->assertGreaterThan(0, $payment->applied);
+        
+        // $this->assertEquals(Invoice::STATUS_PAID, $invoice->status_id);
+        // $this->assertEquals(0, $invoice->balance);
+
+    }
+
+
+    public function testUnappliedPaymentsAreDisabled()
+    {
+        
+        $settings = ClientSettings::defaults();
+        $settings->use_unapplied_payment = 'off';
+
+        $client = Client::factory()->create([
+            'company_id' => $this->company->id,
+            'user_id' => $this->user->id,
+            'settings' => $settings,
+        ]);
+
+        $this->assertEquals('off', $client->settings->use_unapplied_payment);
+
+        $invoice = Invoice::factory()->create([
+            'company_id' => $this->company->id,
+            'user_id' => $this->user->id,
+            'client_id' => $client->id,
+            'auto_bill_enabled' => true,
+            'status_id' => 2
+        ]);
+        $invoice  = $invoice->calc()->getInvoice();
+        $invoice_balance = $invoice->balance;
+
+        $payment = Payment::factory()->create([
+            'company_id' => $this->company->id,
+            'user_id' => $this->user->id,
+            'client_id' => $client->id,
+            'amount' => 100,
+            'applied' => 0, 
+            'refunded' => 0,
+            'status_id' => Payment::STATUS_COMPLETED
+        ]);
+
+        $invoice->service()->markSent()->save();
+
+        $this->assertGreaterThan(0, $invoice->balance);
+        
+        try {
+            $invoice->service()->autoBill()->save();
+        }
+        catch(\Exception $e) {
+        
+        }
+
+        $invoice = $invoice->fresh();
+        $payment = $payment->fresh();
+
+        $this->assertEquals($invoice_balance, $invoice->balance);
+        $this->assertEquals(0, $payment->applied);
+        $this->assertEquals(2, $invoice->status_id);
+        $this->assertEquals(0, $invoice->paid_to_date);
+        $this->assertEquals($invoice->amount, $invoice->balance);
+
+        // $this->assertEquals($payment->applied, $invoice->paid_to_date);
+        // $this->assertEquals(2, $invoice->status_id);
+
+
+    }
+
+}
\ No newline at end of file