Firebase cloud messaging stopped with upgrade to Oreo

I was just getting started with Android development and managed to get Firebase messaging working after running the wizard. I was able to receive background notifications on my Nexus 5X running Nougat. But then my 5X upgraded to Oreo and Firebase notifications haven't worked since. I've heard about background execution limitations, but since I'm just getting started I don't know what I actually have to do to get it working again. Are there any write ups on this? I tried a new project from scratch hoping the wizard had been updated, but no change. I was using application broadcast messages and topic subscription messages, no device token used.