As a 501c3 you can "book revenue", but your profit is to be limited to 10% or less in related biz income. And about $1,000 in unrelated biz income.
It has been a long time since I was in school that was taught this. But after the limitations, you get taxed.
So not booking revenue is BS. You have to file if over $5,000 in revenue.
Check my work, like I said it has been decades since I dealt with nons.