Fee, donation, alms, whatever. It’s all the same thing. There may not be a set cost, but there is definitely an expectation of a donation. Just like eating out. Nobody is forced to tip, but in reality you have to tip.

Also, OP mentions not regularly attending a Christian church. There’s no specifics. If they were raised Baptist, I have to venture a guess that they would have to accept the teachings of the Lutheran or Catholic dogmas and be indoctrinated into a specific denomination before getting baptized.