@krusoleo @kvhsiteimprove there was an debug error on setting page. because of undefined variable.

It uses WordPress's native settings API, so there's no need to check for the nonce there.
I believe developer added the nonce to avoid WPCS errors. But we can fix it something like this
15f82f4#diff-26cce9fe112352c997c11b2ea5de9c8bL92-L94