I think the problem is the plugin doesn’t support Variable Subscription product types with these extra fields? I tested a standard Variable product and I was able to retrieve the gtin, mpn, and Optimised Title with success.
Debug.log is showing it’s trying to map from the following:
[15] => Array
(
[rowCount] => 15
[attribute] => g:gtin
[prefix] =>
[mapfrom] => custom_attributes__woosea_gtin
[suffix] =>
)
