The INVALID_OR_NULL_FOR_RESTRICTED_PICKLIST error in Salesforce means that you're trying to insert or update a record with a value for a restricted picklist field that:
NULL or an empty value when one is required.Open vs. open) will trigger this error.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.