DNS problem - A recorder NS - MX recorder

hi all
I'm loving the panel, I am gradually learning to work with it, but I'm having trouble with dns.
I need to create a subdomain, mail.c4cwbr.com with but I can not.
another problem is to adjust the nameserver, NS1 and NS2, but even after adjusting for the A recorder is still giving error.
below my settings:


please help me, I do not want to go back to using the sentora.