@cronk005.
The values ylineA and ylineB that you are trying to pass as startValue and endValue are basically an element within $datapoints
array. But you are trying to access it directly, which would be undefined. Accessing the values properly should work fine in this case.
If the issue still persists, kindly share a working sample project along with sample database so that we can run it locally at our end to help you fix the issue.
—
Shashi Ranjan
Team CanvasJS