Q. How do I link my existing non-Caltech Overleaf account with my Caltech account?

Caltech users must use their IMSS (access.caltech) credentials to access their Overleaf accounts. To link your existing Overleaf account to your access.caltech credentials, please use your access.caltech credentials to log in through your institution (green button at very bottom of page). Once logged in, you can link your existing Overleaf account to your access.caltech account. Account linking is a one-time process, but must be done for continued access.

If you are still receiving an error after attempting  the above steps, the problem may be that you have a non-Caltech email address set up as your Caltech access account / official email account. Contact IMSS to change your access.caltech / official Institute email to your @caltech.edu email. It should then link properly.