Thanks for your reply.
I don't see screenshot would help here. All you can see is a stacked chart without labels.
Here is more information:
The chart is a stacked bar chart with only one expression and two dimensions (month in the x axis and another dimension for stacking).
When I check the box 'Values on Data Points', I can see the data label on Access Point.
But when I put a variable (1 or 0) into 'Show Value' option under the expression, the data label cannot be seen on Access Point.
My aim is to have control over hide and show of data label on Access Point in such chart.