Add touch screen functionality to WordPress drawing plugin

I'm designing a WordPress website that allows artists to critique each others work. Part of the critique process is drawing over an original image and submitting that revised image as a comment. I'm customizing an existing plugin (Drawblog) that provides most of the functionality I need. Unfortunately Drawblog only works with a mouse not on touchscreen. The artists who will use the site will be interacting with a variety of devices. Most will be using iPads and Apple pencils. I added a function to track touch position. It appears that I have touchstart and touchend working. The canvas will draw dots but not lines. I can't figure out why touchmove isn't drawing. I need someone with experience with Javascript and HTML5 canvas to troubleshoot the issue.