Hi

You are allowed to write 2 papers but only from the combination they allow and you have to pay fees for both. I didn't quite understand the latter half of your question pls clarify

https://gate.iitkgp.ac.in/gate_syllabus.html

"A candidate appearing in ONE or TWO Papers should fill ONLY ONE application form. In case of Multiple applications, only one will be accepted and remaining applications will be rejected without any refund for the paid fee.

A candidate is allowed to appear either in ONE or UP TO TWO papers of the GATE 2022 examination. However, a candidate is only allowed to select the second paper from the pre-defined Two Paper Combination (https://gate.iitkgp.ac.in/two_paper_combinations.html) list."

Hope this helps!