Purchase New Cert or Add New IP Address?

Hi, I'm new to this forum and don't have a lot of experience with whm and cpanel we've got a client that wants to implement reverse billing. The layout as follows with the same service provider current whm server(public ip 10.1.1.1) with domains a.com(old) and b.com(new) then a apn with public ip 10.1.1.2 which points to 10.1.1.1 when I go to b.com all works fine on port 80, 2087 and 2083 the problem been experienced is that when going through https the certificate is invalid and complains it's resolving to 10.1.1.2 which is the apn Do I need to purchase a new certificate or add a new ip to this whm server and assign the b.com domain to it the message I get when going to cpanel for b.com ssh status The domain b.com resolved to an IP address "10.1.1.2" that does not exist on this server.