I’m trying to delete these cookies when users revoke the required consent, but unable to delete. What could be the reason?
how are you trying to delete those cookies? There is a function to achieve that:
you can also check if cookies are present, disable them so no new cookies are created with the next tracking request and a few other things. API — Piwik PRO Analytics Suite 16.23 documentation has everything you need to know.
Hope that helps,