I use a domain that I bought from Ionos and I used Cloudflare for my SSL. But since yesterday I can’t receive any mails with my business email account (the mail account is made with Google Business using my domain).
Has anyone an idea how to fix this? Is this an Cloudflare problem?
Are you saying your server does not have a certificate?
In that case you have an actual security issue and should fix that straight away.
Pause Cloudflare and contact your host to fix the server. Your host should also assist you with your email, as Cloudflare does not handle email at all.