Hi Lewatle,
This looks like a possible configuration error to me. After registering, users should be send to the `/register` path in the *DSpace User Interface*. However, the error you shared looks like it's creating links that start with `/server/register` (which would be the DSpace REST API and not the User Interface).
I suspect that your "dspace.ui.url" is misconfigured in your backend's local.cfg or dspace.cfg. It may be specified with "/server" (which would be incorrect as that would send users a registration link that goes to the REST API instead of the User Interface).
Tim