It seems like the issue you’re facing with the ValueFormatString not working is due to the case sensitivity. The correct property name is valueFormatString in camelCase, not ValueFormatString. Please try updating it to valueFormatString and check if that resolves the problem. Please take a look at this JSFiddle for working code. If the issue persists, kindly create a JSFiddle reproducing the issue & share it with us so that we can look into the code/chart-options being used, understand the scenario better and help you out.
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Vishwas R
Team CanvasJS