Store data in custom fields from Mailchimp after a WooCommerce order

We’re looking for someone who’s very familiar with MailChimp and who can fill Custom Fields after a WooCommerce order.

We’re currently using the official WordPress plugin “Mailchimp for WooCommerce” and our goal is to store a coupon code in a custom field in MailChimp after placing an order.

Unfortunately, it didn’t work with the “mailchimp_sync_user_mergetags” filter.

Then we tried to fill this field with a webhook after placing an order. Unfortunately, for some reason, this webhook never runs.