diff --git a/lnbits/core/models.py b/lnbits/core/models.py
index 0ee39618c..e802c2f8d 100644
--- a/lnbits/core/models.py
+++ b/lnbits/core/models.py
@@ -72,7 +72,7 @@ class Payment(BaseModel):
     pending: bool
     amount: int
     fee: int
-    memo: str
+    memo: Optional[str]
     time: int
     bolt11: str
     preimage: str