I am using SuiteCRM 7.6.4.
I have a couple of custom modules similar to contacts & leads. I have created custom fields for Duplicate Check while importing, however, while importing on the last step where we need to select the fields available for the Duplicate check, it is empty. I have enabled my custom fields for duplicate check, but its not reflecting under the imports option.
I had the same problem and managed to find this https://developer.sugarcrm.com/2011/11/08/whats-new-in-sugar-6-3-import-duplicate-fields-checking/
In summary you need to create an index for the field that you want, that means going to the database and executing SQL command -
ALTER TABLE accounts_cstm ADD INDEX newTextIndex(newText)
change ‘account_cstm’ to table and ‘newText’ to the field you want.