DMA interrupt not firing with Zero DMA demo

First off, I'm using a Sparkfun SAMD21 breakout board, not a Zero, so it's possible that is why I'm running into problems. However, I have been able to use other code that enables interrupts, so I'm a bit confused.

I am trying to load the demo from this thread: SPI write with DMA - Arduino Zero - Arduino Forum

All of the setup works fine, but the interrupt never fires. The code would otherwise be perfect for what I am doing if I could get that working.

Any help is appreciated!

As an aside, I'm primarily a hardware/FPGA guy. This is my first real foray into Arduino and C/C++.