Configure dns-o-matic with Cloudflare

I (a beginner) have just created a Cloudflare Zero Trust account with the intention to use some safer dns servers in my router. This is for personal use in a home network where I have dynamic ip’s from my ISP. My issue is how to configure dns-o-matic. There are 4 settings but 2 of them I am not sure what to enter:
Hostname: I read somewhere that I can enter “dynamic”.
Domain: Here I don’t know what to enter.
Can anybody assist me? Thanks.

Nobody care to comment? Do you have to have your own domain to use a Cloudflare Zero Trust account?