Hi does anyone know what i have to modify to group my contacts by Tag?

I tried to edit the search view. But get an Error. The tag field is call category_id.
but when i add a line in the search view like:

<group expand="0" name="group_by" string="Group By">

                       <filter name="salesperson" string="Salesperson" domain="[]" context="{'group_by' : 'user_id'}"/>

                       <filter string="Company" context="{'group_by': 'parent_id'}"/>

                       <filter string="Country" context="{'group_by': 'country_id'}"/>

  <filter string="Tag" context="{'group_by': 'category_id'}"/>

                   </group>

I get the error

AssertionError: Fields in 'groupby' must be regular database-persisted fields (no function or related fields), or function fields with store=True