Hi! First of all, thanks for your support and sorry about that inconvenience.
Unfortunately I don't have a Mac to replicate the problem but I leave you this link where it explains step by step how to open a file that gives you that error message: https://www.macworld.co.uk/how-to/mac-software/mac-app-unidentified-developer-.
Please, let me know if this works. If not, I'll put an order for you to get a refund.