One or more of the PivotTables chosen have "Include new items in manual filter" selected for the field corresponding to this ...

One or more of the PivotTables chosen have "Include new items in manual filter" selected for the field corresponding to this slicer. Slicers can only be used with fields where "Include new items in manual filter" is not selected. Click OK to unselect "Include new items in manual filter" for this field and connect the PivotTables.