diff --git a/src/pretix/plugins/paypal2/client/core/environment.py b/src/pretix/plugins/paypal2/client/core/environment.py
index 2be81982a..d8740b4c1 100644
--- a/src/pretix/plugins/paypal2/client/core/environment.py
+++ b/src/pretix/plugins/paypal2/client/core/environment.py
@@ -37,7 +37,7 @@ class PayPalEnvironment(VendorPayPalEnvironment):
                     'payer_id': self.merchant_id
                 },
                 key=None,
-                algorithm=None,
+                algorithm="none",
             )
         return ""