[ISG REST Testing] Getting a correct response but error log captures error

I am posting a json request and I'm getting a correct response (201 code and data returned is correct). But SoapUI logs something like NamespaceConflictException "Attribute prefixes must be declared"

Does this have to do with my request (syntax error)? Or this is something related to the code of the REST service?

This is my first time testing REST so apologies if this is a stupid question.

Thanks in advanced!