The most likely reason that you’re receiving an error message is that ‘forgot?’ was clicked more than once and you have opened an email from an earlier click rather than the most recent. If you were to click the ‘forgot?’ link twice for example, the second email you receive would be the one you’d need to use to reset your password. The password token linked to the first email would be invalidated by the newer one.
Alternatively, please check that the URL you are requesting the password reset from is the same as the URL for your dashboard i.e. if you're using our new dashboard you would need to request a reset link via https://manage.gocardless.com. If you're still using our previous dashboard the URL would be https://dashboard.gocardless.com. If you're requesting the reset link via the wrong URL you will not be able to successfully complete the password reset flow.