diff --git a/src/Payment.php b/src/Payment.php
index aeefd76..5a43380 100644
--- a/src/Payment.php
+++ b/src/Payment.php
@@ -88,7 +88,7 @@ public function getPaymentUrl()
             throw new InvalidInvoiceIdException();
         }
 
-        $signature = vsprintf('%s:%01.2f:%u:%s', [
+        $signature = vsprintf('%s:%01.2F:%u:%s', [
             // '$login:$OutSum:$InvId:$passwordPayment'
             $this->login,
             $this->data['OutSum'],