Fix BPA registration error message issue

[minh-biocommons]

Description

Short update to fix BPA registration error message issue

Changes

• Updated response error message sent to the front end
• Update related tests

Checklist

• I have commented my code, particularly in hard-to-understand areas
• I have added unit / integration tests that prove my fix is effective or that my feature works
• I have run all tests locally and they pass
• I have updated the documentation (if applicable)

[marius-mather]

Yep, looks good.