MX records error

I’m trying to setup email routing but I keep getting an error message:
Non-Cloudflare MX records exist (Code: 2008)
I’ve waited 2 hours since deleting the old MX records at my domain registrar IONOS, updating the MX records as specified by CF, but it keeps saying the same error. I’ve also tried resetting nameservers to see if that affects anything (away from CF).

If the Authoritative nameservers are Cloudflare, then you need to delete the old MX from the Cloudflare dashboard.

Nothing you do with IONOS DNS will make any difference if they are not authoritative for the domain, as no client will ever attempt to use their nameservers.