This page documents known developer concerns with the
Classroom add-ons API.

## Error messages

Most errors are covered in the descriptions of specific methods in the
[reference documentation](https://developers.google.com/workspace/classroom/reference/rest). Some errors are [specific to add-ons](https://developers.google.com/workspace/classroom/reference/addons_errors).

If you're unable to troubleshoot an error on your own, reach out to your Google
contacts for support.

## CourseWork API compatibility

See the [Create attachments from a third-party site](https://developers.google.com/workspace/classroom/add-ons/get-started/attachments-journey#create-attachments) guide to creating add-on
attachments through a CourseWork flow.

## Pop-up blockers

The add-on sign-in flow can be disrupted if the end user has enabled a pop-up
blocker. See the [manage pop-up blockers section of the frictionless sign-in
page](https://developers.google.com/workspace/classroom/add-ons/developer-guides/frictionless-signin#manage_pop-up_blockers) for more information about how to implement the sign-in flow in the event
that end users enable pop-up blockers.

## Multi-login

Multi-login is not supported for add-ons. See the [multi-login section of the
frictionless sign-in page](https://developers.google.com/workspace/classroom/add-ons/developer-guides/frictionless-signin#multi-login) for more information about multi-login issues and
possible workarounds.