Most people think that if you use Google Calendar, you need to use it with a Gmail email address. Fortunately, this is not true. You can create a Google Calendar account on any email address without using G Suite. This is quick and simple and does not require any domain setup whatsoever.
Creating a Google Calendar account for your non-Gmail email address
Go to https://accounts.google.com/NewAccount and create a Google Account for your business email address or any other email address that you would like the Google Calendar account to use.
Immediately after that, go to https://www.google.com/calendar and configure the new calendar. Make sure that your business email address is showing on the right corner of the Google header.
Make sure not to create a Gmail account - create a calendar only.
That's it. You now have a Google Calendar account for your business email address and you can connect this Google Calendar to OnceHub. All Google Calendar invites that originate from the Google Calendar account will now come from your business email address.