Cant assign materials to my particle system

First off, I’m 100% green to Unreal, coming over from Unity so I’m relearning a lot.
Trying to follow along an FPS tutorial and building a muzzle flash for a gun. But every time I try to assign a material to the particle system, it remains “None”. I should note that this is a pre-made asset for the tutorial maker. That said, I have tried assigning the exact same material as the original and even every other material available and nothing sticks. I even tried mimicking the original file structure, nothing works.

I’ve seen this has been a common problem in the past 5 years but I haven’t seen many solutions.

Any thoughts friends?

Can you show a pic of the material in the content browser and where you’re trying to drag it to?

( Does it have a green underline in the content browser? )

Yes! All the slots are green, and even the materials in the content folders have a similar green bar on the bottom of their thumbnail. I initially just assumed that it was a way of color coding similar purposed/compatible assets to streamline the process.

I think it’s something to do with the particle system itself. I mean, why does it have 500 material slots?