diff --git a/app/DataMapper/CompanySettings.php b/app/DataMapper/CompanySettings.php
index 39662af39b53..aa9bb7064d34 100644
--- a/app/DataMapper/CompanySettings.php
+++ b/app/DataMapper/CompanySettings.php
@@ -29,7 +29,7 @@ class CompanySettings extends BaseSettings
 
     public $besr_id = ''; //@implemented
 
-    public $lock_invoices = 'off'; //off,when_sent,when_paid //@implemented
+    public $lock_invoices = 'off'; //off,when_sent,when_paid,end_of_month //@implemented
 
     public $enable_client_portal_tasks = false; //@ben to implement
 
diff --git a/app/Http/Controllers/InvoiceController.php b/app/Http/Controllers/InvoiceController.php
index 79e348288788..c307e6302d01 100644
--- a/app/Http/Controllers/InvoiceController.php
+++ b/app/Http/Controllers/InvoiceController.php
@@ -408,7 +408,7 @@ class InvoiceController extends BaseController
         }
 
         if ($invoice->isLocked()) {
-            return response()->json(['message' => ctrans('texts.locked_invoice')], 422);
+            return response()->json(['message' => '', 'errors' => ['number' => ctrans('texts.locked_invoice')]], 422);
         }
 
         $old_invoice = $invoice->line_items;
diff --git a/app/Http/Requests/Invoice/UpdateInvoiceRequest.php b/app/Http/Requests/Invoice/UpdateInvoiceRequest.php
index 0e75760a6612..961fcb52ca68 100644
--- a/app/Http/Requests/Invoice/UpdateInvoiceRequest.php
+++ b/app/Http/Requests/Invoice/UpdateInvoiceRequest.php
@@ -67,7 +67,7 @@ class UpdateInvoiceRequest extends Request
         $rules['client_id'] = ['bail', 'sometimes', Rule::in([$this->invoice->client_id])];
         $rules['line_items'] = 'array';
 
-$rules['discount'] = 'sometimes|numeric|max:99999999999999';
+        $rules['discount'] = 'sometimes|numeric|max:99999999999999';
         $rules['project_id'] = ['bail', 'sometimes', new ValidProjectForClient($this->all())];
         $rules['tax_rate1'] = 'bail|sometimes|numeric';
         $rules['tax_rate2'] = 'bail|sometimes|numeric';
@@ -80,7 +80,7 @@ $rules['discount'] = 'sometimes|numeric|max:99999999999999';
         $rules['partial'] = 'bail|sometimes|nullable|numeric';
         $rules['amount'] = ['sometimes', 'bail', 'numeric', 'max:99999999999999'];
 
-$rules['date'] = 'bail|sometimes|date:Y-m-d';
+        $rules['date'] = 'bail|sometimes|date:Y-m-d';
 
         // $rules['partial_due_date'] = ['bail', 'sometimes', 'exclude_if:partial,0', Rule::requiredIf(fn () => $this->partial > 0), 'date', 'before:due_date'];
         // $rules['due_date'] = ['bail', 'sometimes', 'nullable', 'after:partial_due_date', Rule::requiredIf(fn () => strlen($this->partial_due_date) > 1), 'date'];
diff --git a/app/Http/ValidationRules/Invoice/LockedInvoiceRule.php b/app/Http/ValidationRules/Invoice/LockedInvoiceRule.php
index e6aa6d445216..6a4d6ac198c2 100644
--- a/app/Http/ValidationRules/Invoice/LockedInvoiceRule.php
+++ b/app/Http/ValidationRules/Invoice/LockedInvoiceRule.php
@@ -16,6 +16,7 @@ use Illuminate\Contracts\Validation\Rule;
 
 /**
  * Class LockedInvoiceRule.
+ * @deprecated
  */
 class LockedInvoiceRule implements Rule
 {
@@ -67,6 +68,13 @@ class LockedInvoiceRule implements Rule
                 }
 
                 return true;
+
+            //if now is greater than the end of month the invoice was dated - do not modify
+            case 'end_of_month':
+                if(\Carbon\Carbon::setTimezone($this->invoice->company->timezone()->name)->parse($this->invoice->date)->endOfMonth()->lte(now()))
+                    return false;
+
+                return true;
             default:
                 return true;
         }
diff --git a/app/Models/Invoice.php b/app/Models/Invoice.php
index 135f420ed8f5..70dfd979a814 100644
--- a/app/Models/Invoice.php
+++ b/app/Models/Invoice.php
@@ -563,6 +563,8 @@ class Invoice extends BaseModel
                 return $this->status_id == self::STATUS_SENT;
             case 'when_paid':
                 return $this->status_id == self::STATUS_PAID || $this->status_id == self::STATUS_PARTIAL;
+            case 'end_of_month':
+                return \Carbon\Carbon::parse($this->date)->setTimezone($this->company->timezone()->name)->endOfMonth()->lte(now());
             default:
                 return false;
         }
diff --git a/lang/en/texts.php b/lang/en/texts.php
index 003509f2c939..375bfbf5ecb3 100644
--- a/lang/en/texts.php
+++ b/lang/en/texts.php
@@ -5334,6 +5334,7 @@ $lang = array(
     'btcpay_refund_body' => 'A refund intended for you has been issued. To claim it via BTCPay, please click on this link:',
     'currency_mauritanian_ouguiya' => 'Mauritanian Ouguiya',
     'currency_bhutan_ngultrum' => 'Bhutan Ngultrum',
+    'end_of_month' => 'End Of Month'
 );
 
 return $lang;
\ No newline at end of file
diff --git a/tests/Unit/DatesTest.php b/tests/Unit/DatesTest.php
index 3f5ca6e2d4dd..a8cf2ea96345 100644
--- a/tests/Unit/DatesTest.php
+++ b/tests/Unit/DatesTest.php
@@ -31,6 +31,29 @@ class DatesTest extends TestCase
         // $this->makeTestData();
     }
 
+    public function testDateNotGreaterThanMonthsEnd()
+    {
+        $this->travelTo(now()->createFromDate(2024, 6, 20));
+        $date = '2024-05-20';
+        
+        $this->assertTrue(\Carbon\Carbon::parse($date)->endOfMonth()->lte(now()));
+
+        $this->travelBack();
+
+    }
+
+    public function testDatLessThanMonthsEnd()
+    {
+        $this->travelTo(now()->createFromDate(2024, 5, 30));
+        $date = '2024-05-20';
+        
+        $this->assertFalse(\Carbon\Carbon::parse($date)->endOfMonth()->lte(now()));
+
+        $this->travelBack();
+
+    }
+
+    
     public function testLastFinancialYear3()
     {
         $this->travelTo(now()->createFromDate(2020, 6, 30));