The steps below show how to migrate to the ShopSync app to continue using the "Mailchimp eCommerce" integration within the OCU app:
1. Follow the steps in this article from Mailchimp to switch your integration, and its automations, from the Mailchimp for Shopify app to the ShopSync app: https://mailchimp.com/help/switch-shopify-shopsync/
2. Once you have successfully migrated to the ShopSync app, delete the Mailchimp for Shopify app from your store.
3. Within the OCU app, head to Settings > CRMs > Mailchimp to disconnect and then re-connect the "Mailchimp eCommerce" integration option so that it can work with the ShopSync app instead.