Invalid or Null for Restricted Picklist [INVALID_OR_NULL_FOR_RESTRICTED_PICKLIST]

This error is shown when you try to Insert / Update a Picklist field with values that are not listed as 'Active' on the Picklist field, and 'Restrict picklist to the values defined in the value set' is set to True.

ECE_SForceDataError: We got an error back from SalesForce when trying to update or insert data in SalesForce: Error returned from SFDC on create: [fields: CountryCode , message: Country Code: bad value for restricted picklist field: KO , statusCode: INVALID_OR_NULL_FOR_RESTRICTED_PICKLIST ].

The field has been set up, so that only certain values can be selected and entered. If this is correct, you will need to fix the data so that only valid values are present. If you still want to enter the values that you are sending from your ERP to Salesforce, then you would need to update your current picklist in Salesforce. Follow these steps here on how to add or update the picklist value -> How to add/update picklist values in Salesforce.