If you bought a domain name you should have control over the A record(s) which point the domain name to IP address(es). Forwarding is not the same thing, it is a service used to automatically redirect requests from the domain name to another location.

If you do not have the ability to add A records then you should contact the host you purchased it from as that rather defeats the purpose of having a domain name.
Either that, or what you have actually purchased is the forwarding service and not a full domain name.


As for the error, the 3xx class of HTTP status codes, as visualAd said, indicate redirection, not an error condition. However, a redirection of a POST request to another domain will usually trigger a warning or error message in the client as it is a sign of a possible malicious hijack and may lead to breach of privacy.