Rails ActiveAdmin reset password token is invalid

I have a Rails API with ActiveAdmin, using this tutorial as a base to get started: https://blog.heroku.com/a-rock-solid-modern-web-stack

When a user chooses the 'Forgot your password?' link in the login (website.com/admin), they're emailed a link to create a new password. After entering the password twice, and clicking the 'Change my password' button, the user gets the following error messages.

1 error prohibited this admin user from being saved:
Reset password token is invalid

Any help on fixing this error would be greatly appreciated, thanks!