Once you name your business in the first step while adding a business in OPPYO, it creates a subdomain for it automatically according to the name. Now, if you do not own a domain and want to run your business on the OPPYO subdomain, you can proceed with the automatically generated subdomain for your business.
But in case, if you want to change the automatically generated subdomain to any other phrase, you can do that. It is not mandatory, it totally depends on your choice.
One thing is here which needs your attention that you can change the subdomain only once, so we suggest you phrase it carefully.