When recording the request is application/x-amf and the response is application/x-amf or application/json but while running the script the assertion are getting failed because the same response content type is text/html. what can be done to solve this?
application/x-amf is the content type for Flex applications. It's the AMF binary protocol. If you did not get the same response type during the replaying it usually means that you did not correlate some of the dynamics values.
I would suggest you to look at the NeoLoad documentation in order to understand how to handle them.
For example, you can look here