Placing a qry parameter into chart legend (1 Viewer)

Access 2016 - I created a good chart, but the query it is based on requires a prompted for parameter - and I would like to have the "entered" query parameter appear as the LEGEND of the chart. However, it is not allowing me to use the query parameter field in the chart wizard.

enter the param on a form text box,
reference it in the chart... forms!myForm!txtBox