Has anyone been in a online relationship where the person wanted to pay for their plane ticket to come and see them?

No, but the moment they ask for money I'd block and move on. I never send money to anyone.

When I was on EP, there was a user who befriended me and then kept messaging me about her "relative" that had "cancer" and needed money for the "medicines".
I let her beg for a while, then I blocked her lol

I always buy train tickets, hotel and dinner for anyone coming to see me.

No, I have not; but I have read and heard plenty of warnings about those frauds, in which the victim is asked to send the money but never sees either the supposed lover or the money again.

I have been offered plane tickets to meet persons here, but have not accepted.

I've been the person to pay for the plane ticket. But not the inverse.

Yes, it's called a scam! Be careful!!

Yes, but no, cheapskate. 😒😅

Yes