Transactions that fail webhook verification should return an error code

[richardmands]

E.g. https://sandbox.kinetic.host/apps/cl9xh05560002li0rmxp33l5i/environments/cl9xh05560005li0re2bebpn0/transactions/cl9y6aawd007lti0sul178zql

This transaction returned a 201 code to the browser but should have returned an error.