Related Questions:
Am I able to filter using the API?
Can I filter for Custom Fields using the API?
Answer:
Filtering by Custom Fields is not supported with the API. The following filters are supported when listing your Bookings via the API:
From within Event Temple you are able to filter the Booking List using Custom Fields, however there is no way to currently automate it.
For more information on the API please check out our Developer's Hub.