This API Token is valid and active BUT 6003 Invalid request headers. Please confirm that you have supplied valid Cloudflare API credentials

Not in regard with your current error message, but it is possible to combine a DNS authenticator plugin with a webserver installer plugin, if you want. See the user guide listed above by Rudy, it contains a section about combining plugins.

Did you also install the appropriate DNS plugin using snap according to the instructions on the "wildcard" tab of the certbot.eff.org instructions?

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