Advice on Updating Google Calendar From Restful API or Webhooks

I used software called Booqable to take customer bookings. It has Restful API & Webhooks. It also supports Zapier. I've been using Zapier to update my Google calendar so each time a customer books it adds it to my Google Calendar. It works OK but there's a few problems. Firstly I'm on the free plan which only allows 100 zaps a month. Secondly, we have 2 warehouses that use separate Google calendars but since there's no branching in Zapier free plan it posts it all to the same calendar & we have to change in manually. To get branching in Zapier I'd have to get the professional plan which is about $100 a month. I have been playing with Integromat but it doesn't directly support Booqable. I was thinking of just getting all the transactions into a Google Sheet & using that to trigger the calendar posting. Anyway I need someone to give me some advice on the best way to do this. You don't have to do it. just give me advice. I would post another project to implement it. I did have another Freelancer working on getting the bookings into Google sheets but the solution he came up with was incredibly complicated & involved setting up a local server.