I am trying to host the webapp and the company page under one domain like
Google has
https://www.google.com/ https://support.google.com/
I thought it was two different domains and I've searched for abc.myfirm.io (example) and it does not look like I need to purchase a domain to have that setup.
I am currently using NameCheap
You do not need to register a separate domain with a domain name registrar. You can just create a DNS entry for the subdomain. If the different domains are all aliases for the primary domain (myfirm.io), then use a CNAME
record to point the subdomains to myfirm.io. If they are intended to be separate services, create an A
record to point the subdomain to the IP it's hosted on.