Error messages are not landing in the DLQ

[Hooghof]

Describe the bug
I expect that the error that this flow produces will land in the DLQ, like it happens on 4.17.10.

To Reproduce
curl --location 'https://next.dovetail.world/test/inbound_http/regressiontests/DeadLetter' \ --header 'Content-Type: application/xml' \ --data '<root>DLQ</root>'

Flow
Instance: next
Tenant: Regression Tests
Flow: DeadLetter

Screenshots
Not applicable.

[skin27]

I already created a backend change, but this also needs a frontend change:

https://github.com/fluxygen/front-end/issues/6224