I run a web service with email validation, and a nontrivial number of users' validation emails bounce with a request to click some link to pay some money in ord

I run a web service with email validation, and a nontrivial number of users' validation emails bounce with a request to click some link to pay some money in order to email the user. Sometimes I get the same responding to support requests from users. I suspect these same users wonder why such a large fraction of their online interactions/signups don't work...