Payment Gateways Domain Mapping

Domain Mapping is not listing payment methods from WHMCS. I really need help with this ASAP. All IPs are whitelisted in security of WHMCS, with my reseller (Namecheap), and as a restricted IP in WHMCS. There should be no reason this isn't working. Here is the exact error:

Please make sure you have correctly entered your login credentials and save again to retrieve your payment methods.

Reseller API log shows I am successfully logging into WHMCS.