ParceError at [row,col]:[1,1] Message: Contant is not allowed in prolog

I think that Katalon Studio can not handle HTTP Response in MIME Multipart format.

You should either

  1. configure, if possible, your target web server app NOT to respond in MIME Multipart format (you may need to speak to the developers).
  2. use other software that can handle HTTP Response in MIME Multipart format. I made a quick search and found this