return a reason of failed payment to the pos; disable a change of wallet in the form

lnbits/extensions/boltcards/lnurl.py

@@ -136,8 +136,8 @@ async def lnurl_callback(
         )
 
         return {"status": "OK"}
-    except:
-        return {"status": "ERROR", "reason": f"Payment failed"}
+    except Exception as exc:
+        return {"status": "ERROR", "reason": f"Payment failed - {exc}"}
 
 
 # /boltcards/api/v1/auth?a=00000000000000000000000000000000

lnbits/extensions/boltcards/templates/boltcards/index.html

@@ -215,6 +215,7 @@
           emit-value
           v-model="cardDialog.data.wallet"
           :options="g.user.walletOptions"
+          :disable="cardDialog.data.id != null"
           label="Wallet *"
         >
         </q-select>