If you have already sent an invitation to a candidate but they are unable to complete it in the allocated time it is possible to extend it without losing the test invite credit as long as the test is still valid.
If the invitation hasn’t expired, you can resend the invitation and it will prolong the validity of the link to the test. To resend a a test click on the candidate and then on the button ‘Resend email with invitation’.
If you need to extend the validity period of the invitation. You can do that here: Settings >> Company settings >> Validity period. When you press resend the invitation the system will automatically assign the default validity period.