I've created a print service with a custom print template. I'm relatively new to this, so the solution might be obvious but I can't seem to figure it out.
I've added the print service URL to the web application I'm putting together using Web AppBuilder:

The print template that I've created was made in ArcMap and looks like the following:

I had no issues publishing this as a printing service to Server.
When I use the Print widget with no layers on the map (just the basemap), I'm able to successfully run my custom printing service:

However, the problem arises when I add a layer to the map. In the below image, I've added a layer using the Add Data widget:

But when I try to Print using my custom template, I get the error: Error, try again. When I hover over the exclamation point, the message I get is esriJobFailed:

Is there something that I missed when setting up the Printing Service itself? Any documentation to get me going in the right direction would be appreciated.
Thanks