Assign Task to Supplier Contact in Depot Repair

Hi,

A contact has been created from suppliers form in Purchasing. The contact has been assigned an address in contact directory. After creating the supplier contact it has been imported as a resource for CRM with role as Field Service Third Party Service Provider and technician successfully. When trying to assign the task to supplier contact in Repair Order Form Firstly, task cannot be assigned manually. Secondly, when trying to assign task using assignment manager, resource can be found in assignment manager but cannot be assigned to task. This might be a setup issue. Can anyone guide what all setups to