i have a js and php problem

Question

i have this jquery and ajax code that sends data to a php backend which will then be added to a db and rend the response to the ajax callback but the rescponse always come with a html comment tag

"<!-- --> success".... how do i go about it please??#

here is the link to the code:
https://www.sololearn.com/compiler-playground/wEXyb7Z8SDyE