Scope

I am getting the “Field name must start with a 'custom.' prefix” error while setting up custom field mapping on my Retentions account. How can this be fixed?

Solution
It is necessary to use the prefix 'custom' for any custom field name that you are entering on this Chargebee Retention mapping page. This is to differentiate it from the Standard Retentions fields. 

You can enter the value as "custom.field_name”' in the field, and this should fix the issue.