diff --git a/lnurl.py b/lnurl.py
index 4b39374..6ebea46 100644
--- a/lnurl.py
+++ b/lnurl.py
@@ -195,7 +195,7 @@ async def lnurlp_response(req: Request, hit_id: str):
         return {"status": "ERROR", "reason": "Card is disabled."}
     payResponse = {
         "tag": "payRequest",
-        "callback": req.url_for("boltcards.lnurlp_callback", hit_id=hit_id),
+        "callback": str(req.url_for("boltcards.lnurlp_callback", hit_id=hit_id)),
         "metadata": LnurlPayMetadata(json.dumps([["text/plain", "Refund"]])),
         "minSendable": 1 * 1000,
         "maxSendable": card.tx_limit * 1000,
diff --git a/models.py b/models.py
index 5ea4be1..bd044ac 100644
--- a/models.py
+++ b/models.py
@@ -34,7 +34,7 @@ class Card(BaseModel):
         return cls(**dict(row))
 
     def lnurl(self, req: Request) -> Lnurl:
-        url = req.url_for("boltcard.lnurl_response", device_id=self.id, _external=True)
+        url = str(req.url_for("boltcard.lnurl_response", device_id=self.id, _external=True))
         return lnurl_encode(url)
 
     async def lnurlpay_metadata(self) -> LnurlPayMetadata: