Sugar CRM plugin is not working as expected

Your software
My Mautic version is: 4.3.1

We tried to setup a connection between Mautic and sugar CRM.

How it should work:

Sugar CRM is leading sending the following data to Mautic
First Name
Last Name

Mautic is sending back one custom field

Contacts get pushed to Mautic and all fields are updated in one way, also the optin field that should go from Mautic to the CRM.

Contacts are not being synced at all, duplicates are being created.

In general it seems like the setup of the plugin is doing nothing atm, just a push from crm to mautic.