Hi Jarell, sorry to hear about the trouble. Is the output totally blank, or is it just that labels are not printing?
Also, one of the other limitations is that the version of Server that the FeautureLayer is hosted on must be 10.5.1 or later. What version of Server are you using?
Lastly, what happens if you use the AGO printing service?
Here's a sample that prints a labeled FeatureLayer, maybe you can just swap in your layer and test.
The output is totally blank (besides my print template).
I am using 10.6.1.
It seems to print perfectly normal when I'm using the AGO printing service. However it's not working when I'm using the default portal print service and the custom print service.
It sounds like a problem with the print service(s). What do you see in the network traffic when you inspect the response to the export webmap request?
What happens if you just try to print a basemap with the default portal print service or the custom print service?