Using domain as hostname for ssh

I’m currently writing a script using the REST API to automate the process of creating a droplet from a snapshot. I have my own domain for the snapshot (we’ll say it’s example.com) and in the script I map the new IP of the created droplet to sub.example.com through an A record. When using putty, I try to enter sub.example.com as the hostname and it gives me an error saying “hostname not found”. If I try and enter the assigned ip address to the droplet it works. Is there something else I need to do that I’m missing to get this to work? Thanks!