Line markers in area chart are not available, but documentation says they are available

[HamletDRC]

PowerBI Deskttop version 2.50.4859.782 64-bit (September 2017)

Your documentation says that line markers are available in area charts: https://powerbi.microsoft.com/en-us/documentation/powerbi-desktop-accessibility/

I click the area chart -> Visualizations -> Shapes... Customize Series -> ???

The Line Markers widget should be there but it is not. 

Am I doing something wrong here? 

[HamletDRC · Accepted solution]

I found the answer! 

Line Markers are only available when the chart is set to "Categorical" instead of "Continuous". 

Go to Visualizations -> X-Axis... and change the Type field