The issue is a nutshell.

Export customer data from Bigin into zoho sheet.

Create a simple flow that any addition or update in sheet is synced back to Bigin.

You would of thought the data type of the data exported from Bigin would be consistent with the data types for Bigin (such as CompanyNameid is type number) in Flow but the data exported into sheet is type string as Zoho puts zcrm_ at the beginning of the data. so you can't get any flow to work at all. You aways get an error saying the data type is incorrect.