fix migration

backend/database/migrations/2026_06_01_102551_add_client_credentials_to_user_gateways_table.php

@@ -12,7 +12,7 @@ return new class extends Migration
     public function up(): void
     {
         Schema::table('user_gateways', function (Blueprint $table) {
-            $table->string('client_id')->unique()->nullable();
+            $table->string('client_id')->nullable();
             $table->string('client_secret')->nullable();
             $table->integer('status')->default(0);
         });