A user cannot log in

Work through the causes in order rather than resetting the password immediately.

Is the account active?

A deactivated account gives a login failure that looks identical to a wrong password. Check Admin → Users & Staff first.

Are they rate-limited?

Repeated failures trigger a temporary lockout. Wait for the window or clear it from the security screen.

Two-factor problems

A phone clock that has drifted makes every code invalid. Ask them to enable automatic time on the device before you reset enrolment.

IP restrictions

If administrative IP restrictions are on and they are working from home, this is the cause and no password reset will help.