App iframe embed error after successful payment


Monzo payment iframe goes from “switch to app go authorise” to “success” to “error”, exposing some internals and taking some delight away from user experience / confidence that payment was made successfully

Details to reproduce:

  1. Open Amex app
  2. Go through steps to pay by Debit Card
  3. Switch to Monzo app to authorise
  4. See iframe for Monzo payment go from “success” to error that exposes some internals

Observed this a couple of times in the last month. Wasn’t an issue before.

OS: 15.6
Device: iPhone 11
App Version: 4.43.0


Looks like a Java error, and Monzo primarily uses Go on the backend.

Most likely this is an AmEx error, mishandling the 3DS response from Monzo.


I had this with Amex last week trying to pay a few times. Was with starling debit card, so not a monzo issue. Has worked since with same card but.

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Thanks. Have pinged AmEx about this

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