Map Checkboxes to Campaign Monitor

I have a checkbox field in Gravity Forms with 3 options. The labels are exactly the same as those that exist as a “multiple choice - select many” custom field in Campaign Monitor. I have also mapped that field in Settings > Campaign Monitor > Map Fields.

I can’t seem to get them to map. Nothing gets transferred to Campaign Monitor. The name, email address and additional text field all get mapped as they should.

Any ideas?