Adding a rule in iptables with destination ip that won't resolved to it domain

Iptables use IP addresses internally, if you don't want to see any DNS names when listing the rules, use iptables -L -n - it disables reverse DNS lookup.

Two things to your question. One, as CodePainters noted, you need to use -n switch to see IP address in the listing of iptable rules.

Second thing is, iptables process rules in an order. If some previous rule forbade the connection, then adding another rule (-A adds at the end of the chain) will not help. You need to analyse the whole configuration, not just a single rule.