Impossible to create CNAME in OVH DNS


I try to add a custom domain for a website.
The website is not published to date, so I have no link to share. I need my cutom domain to be able to publish.

In the registrar, I had been able to add both 4 values, and TXT value.
But, when I try to add the CNAME value, it says me :
The subdomain is already using a DNS record. You cannot register a CNAME field due to an incompatibility. Delete the existing records for this subdomain, so you can add one, of type CNAME.

There is already a CNAME but for a subdomain for emails, and I CANNOT delete hime.

Does anyone have any idea on how to create another CNAME with the webflow value ?

Thanks in avdance for the help !