I spent the better part of a week trying to get google cash working - submitted passport, utility bills - they kept claiming my passport picture wasn't clear enough. Eventually I gave up and just used paper cash - which is what we, a pretty much 100% highly technical office, use to pay each other.
I love venmo - it's worked well for me. And I use Apple pay multiple times a day, every day. And been a PayPal user for 15 years - but no common thread with colleagues in the office. We just need something that we can be certain everyone can use. Zelle might be that thing.
In a similar anecdote, all 32 members of my law school section use Venmo to submit section dues and dispurse refunds from those dues when someone hosts a gathering, etc. A large group of non-technical users signed up without blinking.
Apple Pay in iMessage makes this laughably easy and secure.