You must be looking for your interview on CoderPad. You probably got a temporary link that looks like the one outlined in the pink box in the image below. Unfortunately that link that has expired. We generate these shortened links for interviews because they are easy to read over the phone; however, for security reasons, these shortened links only last one hour.
Contact your recruiter or interviewer and send them a link to this page (https://coderpad.io/error_pad_link_expired). You may need to explain to them that they gave you the "Phone-Friendly Temporary Link" (outlined in the pink box below), and it has expired. Ask them to send you the permanent link to the pad (outlined in the blue box below), or create a new pad.