Fix 500 when saving payment gateway credentials.

Implement the missing SettingsController::persistGateway method so merchant Paystack/Flutterwave/Hubtel keys can be saved, and cover create + keep-blank-secrets paths with tests.

app/Http/Controllers/Pos/SettingsController.php

@@ -8,6 +8,7 @@ use App\Models\PosLocation;
 use App\Models\PosMember;
 use App\Models\PaymentGatewaySetting;
 use App\Models\PosTable;
+use App\Models\User;
 use App\Services\Import\CrmProductImportService;
 use App\Services\Import\MerchantCatalogImportService;
 use App\Services\Payments\MerchantGatewayService;
@@ -118,6 +119,47 @@ class SettingsController extends Controller
         return back()->with('success', 'Settings saved.');
     }
 
+    /**
+     * Upsert merchant gateway credentials for the acting account.
+     * Blank secret fields keep the previously stored encrypted values.
+     */
+    protected function persistGateway(Request $request, User $user): void
+    {
+        $ownerRef = (string) $user->public_id;
+        $existing = PaymentGatewaySetting::query()->where('owner_ref', $ownerRef)->first();
+
+        $provider = trim((string) $request->input('gateway_provider', ''));
+        $publicKey = trim((string) $request->input('gateway_public_key', ''));
+        $secretKey = trim((string) $request->input('gateway_secret_key', ''));
+        $webhookSecret = trim((string) $request->input('gateway_webhook_secret', ''));
+
+        // No provider chosen and no prior config — nothing to persist.
+        if ($provider === '' && $existing === null) {
+            return;
+        }
+
+        $attributes = [
+            'provider' => $provider !== '' ? $provider : $existing->provider,
+            'is_active' => $request->boolean('gateway_is_active'),
+        ];
+
+        // Leave blank on the form means "keep the saved credential".
+        if ($publicKey !== '') {
+            $attributes['public_key'] = $publicKey;
+        }
+        if ($secretKey !== '') {
+            $attributes['secret_key'] = $secretKey;
+        }
+        if ($webhookSecret !== '') {
+            $attributes['webhook_secret'] = $webhookSecret;
+        }
+
+        PaymentGatewaySetting::query()->updateOrCreate(
+            ['owner_ref' => $ownerRef],
+            $attributes,
+        );
+    }
+
     public function storeTable(Request $request): RedirectResponse
     {
         $data = $request->validate([