On interface it works, but returns an unknown and non debuggable error only when testing on the portal url

The error message points toward an internal issue. I suggest to open a support case.

But, the first thing Appian will ask for, is a code snippet which reproducible shows that error. My approach is to reduce that interface to the minimal version still showing the error. I try to embed as much code directly instead of calling expressions.

The error message points toward an internal issue. I suggest to open a support case.

But, the first thing Appian will ask for, is a code snippet which reproducible shows that error. My approach is to reduce that interface to the minimal version still showing the error. I try to embed as much code directly instead of calling expressions.