Answer
Onboarding invitation links can only be used once and expire after 24 hours. If you click the link and see the message We couldn't sign you in, the link has either already been used or it has expired.
If You Have Already Set a Password
You do not need to use the link again. Go to the online app login page and sign in with your email address and password. Use the Forgot Password link on that page if you need to reset it.
If You Have Not Yet Set a Password
Ask the payroll administrator to resend the invitation. The steps differ depending on which app they use.
In the online (web/mobile) app: Open the employee record and go to Employees >> Details >> Online Portal. Click Resend Employee Portal Email. A fresh invitation is sent immediately to the employee's email address.
In the desktop app: Open the employee record and go to the Online Portal tab. Click Resend Portal Setup Email. The employee receives a new email containing their username and a password reset link.
Once you receive the new email, open the invitation link promptly. The link expires after 24 hours and can only be used once, so do not open it in multiple browser tabs or click it more than once.
For more information on how portal accounts are created, see What Generates An Employee Portal Account and Email?