I am trying to accept an invitation to review a manuscript but it doesn't work

You have received an invitation to review a manuscript and you are prompted for a password.  See how to accept the invitation and start reviewing the manuscript. 

a) Do you already have a Frontiers account?

Yes! Login to your account and accept the review invitation.

No? Creating an account on Frontiers is necessary to ensure that only people involved in the review process have access to the review forum, and hence the authors' findings. You can register here

b) Is the invitation sent to a different email, than the one you've used for your Frontiers' account?

Add a secondary email in your profile, before accepting the review invitation. Linking your email addresses to your account.