On what planet does being sent $20 prove that someone is trustworthy and won’t cheat? I’m genuinely curious. Perhaps look at their interactions and ask questions that provoke critical thinking. Failing at that I’d definitely call the cops because because if this guy does actually exist he’s a sexual predator.
A 16 year old should most definitely not be on grindr. You have to sit him down and talk to him and tell him how unsafe that behaviour is for him. You may have to scare him a little but under no circumstances should you let him go meet this predator. That’s under the assumption that this guy is even gonna meet your cousin or he’s just trying to scam a kid out of money. Sit down with him and tell him to ask this “sugar daddy” why the gift card will prove his loyalty. Maybe make up a family member in law enforcement and have your cousin mention them, this might scare the guy off. No matter what happens don’t let him go though
Oldest trick in the book… It’s definitely a scam. Never send money to receive it or some. I travel a lot in Asia, and these tricks is very common here. Friends I know, experience these things on dating sites all the time.