And now that I think about it, I dont believe there was a contract involved. Just a verbal agreement
These days, you'd be informed in writing, e.g. by email. Usually.
I never charge for my 'gigs' (which I do monthly) because I just want to spread the Word (the word about classical music, that is) but I once did an impromptu Christmas gig in the same venue, when I was contacted frantically less than 8 hours before the concert, and asked to accompany the singing of the choir (which was the audience), because their regular accompanist had fallen ill.
Of course I agreed, even though I was told I'd be playing what the audience wanted to sing, which assuredly wasn't Weihnachts-Oratorium or Messiah, not even Cantique de Noël. No, it was going to be mainly pop songs linked to Christmas, plus a few carols. It turned out that most of those songs only had very tenuous connection to the festive ('religious') season and pretty much all of them were unknown to me. My sight-reading and improvising skills were sorely tested, and some of my latter (based on lead sheets or guitar chords in the songbooks I was given on arrival) raised more than a few eyebrows. (Actually, they were probably downright hilarious to pop aficionados who knew the songs). Well, OK, they sounded more like Chopin than Cher (is that the right spelling?), but hey, I'm a classical pianist, so what could they expect?
They didn't offer any 'reward' for my trouble in the email, not even a glass of holy water, but after the concert (during which everyone had a great time, partly because they heard stuff from the accompanist they'd never heard before and probably never will again), the grateful organizers took me into another room and told me to eat as much as I liked from the offerings on the tables: lots of homemade Christmas cakes, mince pies, cookies, chocolate etc. My kind of payment
(I have a very sweet tooth, but I still have all my teeth). And before I left, completely stuffed, they pressed into my arms two huge bottles of vintage champagne as well as a big bagful of various Christmas treats to keep my sugar levels up until the New Year. It was a profitable evening for me.
But no mention of whether the champagne had been blessed........
(luckily, I'm a teetotaller.)