Parse HTML return from payment provider

Hi
 I have an web form application on which I needed to communicate with a third party payment application, where in some point, I will have to send information to that third party application using "POST". every thing working fine However, If I pass worng data it (paryment application)return me an HTML with error code.
What is the best practices to parse html return from third party and display custom message in my application,
Regards