Hi @JonathanTAU, welcome!
This is working as expected if the first Call My Sub-workflow node is configuredwith On Error>Continue (using error output) AND the second (nested) Call My Sub-workflow is configured with On Error>Stop Workflow, here is a sample:
the issue is likely caused by configuring BOTH Call My Sub-workflow nodes with On Error>Continue (using error output)
In that case, yes at the main workflow level you won’t receive the actual error message (this might even be a bug),
However, the interesting part is that if you configure the first Call My Sub-workflow node with On Error>Stop Workflow, you will get the error:
I hope this explanation is clear and helps clarify the behavior…