set exchange_rate_id to nullable

database/migrations/2021_06_24_095942_payments_table_currency_nullable.php

@@ -0,0 +1,32 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+class PaymentsTableCurrencyNullable extends Migration
+{
+    /**
+     * Run the migrations.
+     *
+     * @return void
+     */
+    public function up()
+    {
+        Schema::table('payments', function (Blueprint $table){
+
+            $table->unsignedInteger('exchange_currency_id')->nullable()->change();
+
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     *
+     * @return void
+     */
+    public function down()
+    {
+        //
+    }
+}