Setting legendMarkerType as ‘triangle’, and legendMarkerColor as ‘white’ seems to be working fine, and creates a dashed line legend marker. You can take a look this JSFiddle for the complete example.
If you are still facing any issue, please share a JSFiddle reproducing your use case, so that we can look into it and help you out.
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Ananya Deka
Team CanvasJS
