rDNS/PTR = FAILED

I know this is a problem I need to resolve with my ISP. But I have a couple questions, please forgive me. I am not a server pro or even well versed in server configuration. I have a very basic skill set.
When I call me ISP and tell them I need them to configure the rDNS for my domain name, is it the domain name like domain.com or my server name like server.domain.com?
Also, once i get my server up and going I will have 3 domains on it. Will I need to have my ISP set up rDNS for each domain or is one enough to make it work. Im am a little lost on this topic.
TIA
Steve

mydomain = domain.com
myhostname = server.domain.com
Thats my settings but the domain is the actual name, i deleted it out for some reason here.

It is expected that the FQDN of the server has rDNS (PTR record). So, in your example it is server.domain.com. You do not need ALL domains hosted on the server to have rDNS -- just so long as you have that main A record as resolvable forward & backward.

Today I called my ISP to have the FQDN set for rDNS. Are you saying that my hostname should be the rDNS? Now I have a larger problem while waiting for propagation my Apache quit working so I am working through that. Trying to get it to restart.

Your server FQDN (fully qualified domain name) is your server's hostname + domain name. Example: srv1.yourdomain.com -- The hostname is actually just "srv1" and the domain name is "yourdomain.com". For proper mail delivery. your server's FQDN should be a forward DNS A record that is resolvable on the public internet. And your ISP or colocation/VPS provider handles the PTR (rDNS) records for their netblock, since it is looked up via IP address. Mail servers interacting with your server expect to check your DNS forward & backward to confirm its identity. It's the biggest factor required for mail delivery to succeed (but now you also have to worry about SPF records, DKIM / DMARC...)

Feel free to post your journal snippet pertaining to your Apache error, or the specific error you are encountering and we can try to help you with that.