Hi calvinseng,
Thank you for your purchase.
 
The issue is that you can not create chart with two string type columns, like you can see in the notice.

When you are creating charts first column that you add should be String column type and second should be Integer or Float column type for Pie charts or Donut chart. For other charts that are supporting more than two columns first should be String column type and other columns should be Integer or Float. In you case you added one column that is Date column type and one that is String column type and chart can't be created without numeric column.
For charts please take a look at documentation from our website - Link