keeping getting a 404 error

Hi, I am trying to finish setting up the conversions API server side for Meta ads, I've been following a YouTube video which has been easy enough to follow, however when clicking the link to ConversionsApiGatewayInstanceURL I keep getting a 404 page. What am I doing wrong? I've checked the new dns is working correctly but it won't let me continue with the set up. Any help would be gratefully received as I'm currently losing the will to live!! Thanks in advance.