I thought that almost all (Blesta, Boxbilling , ClientExec , etc) of them were similar to the WHMCS market ... only different in UI ...
perhaps you can mention what an example of Billing Software looks like which is not similar to WHMCS.
I am very grateful if the password is stored securely.
but it is good if it can use Api Tokens as well as authentication to the server.
Since passwords are a person's privacy, most hackers who get it will save them and then turn them into bruteforce tools.