I've had a homeless person ask me to send them money with Zelle before. I told him my bank doesn't support Zelle (which is true) and he was confused and asked me to double check... That whole situation was awkward.
I've stopped giving excuses as justification for people asking for money from me on the street. I just say "no, sorry" and keep walking. I think it's the most respectful thing I can do. I'm not going to give them money, so the best thing I can do is also not waste their time trying to weasel my way out of it.
I haven't seen this from a homeless person, but it did happen with someone taking donations to a tin on a street. I was so surprised I paid him with a card just because he made me laugh.