I think the 30 minute timer, trying when he was younger, the attempted reward system ... probably has made him a bit anxious. We sometimes do that inadvertently.
Here's some tips that worked for me:
- I had a couple of potties, and I kept them right next to where my boys were playing. So one right next to the train table if they were playing there. Way more success than if they had to run to another room. They are busy playing, not paying attention to their bladders.
- I had them just wear their underwear - no pants. And when we did get a bit experienced, I kept it to pull on pants so they easily could get them down.
- Mine usually pooped when they peed, so sometimes I just let them sit on the potty and read a book, or even watch a show if that helped them stay seated for a while. This phase only lasted a short while (a week) but they put two and two together
My kids all got it over the course of 2-3 days (we always picked a long weekend) then daycare continued it and it was done by the end of a week.
I did not do big rewards. Maybe some M&Ms to start with. Just "Yay! good for you!" to begin with, but we made it no big deal, so that if they did pee down their legs, they didn't feel like they'd let us down.
If he doesn't get it, maybe have him back into pull ups for a month or so and try again when you see he is more ready.
Good luck :)