Hi!!
It may depend on what model air purifier you have, but with just the brand and the fact that it's a HEPA purifier, I looked the device up on Amazon and found this:
https://www.amazon.com/Febreze-FHT170W-HEPA-Type-Tabletop-Purifier/dp/B00OE7P5CI?th=1
I had a hunch, but if you take a look at the product description, you can see for sure that this device uses scents.
View attachment 59659
Now, I'm not sure if you're using this exact model of air purifier or a different one, but I think it's probably pretty safe to assume that they all "add a fresh scent," given the Febreeze brand.
Scents of ANY kind are not safe for birds. Air fresheners (like Febreeze) are definitely dangerous. Even something natural, like essential oils, can quickly become harmful, but synthetic scents like Febreeze are famously unhealthy for birds (and actually, they're not good for cats & dogs either!!!)
You don't need a fancy air purifier by any means, just a HEPA air filter. Most secondary features, like scents or ionizers, are harmful... so the simpler, the better. I personally use a Levoit:
https://www.amazon.com/LEVOIT-Purifiers-Freshener-Core-Mini/dp/B09GTRVJQM/