Just ignore the paypal side.
I think the issue is from the s2member itself.
When runninng server check file, it says:
Although NOT required, s2Member recommends that your WordPress installation be configured with a matching HOST name. This can be changed in the Dashboard, under: WordPress -› Settings -› General -› WordPress/Site URLs. Your current configuration does NOT match: domain.com
Current url setting in wordpress is https://www.domain.com
Any idea how to resolve that?