>>76503730
It's a subcutaneous injection, so you don't want to hit your muscles. It goes into the fatty layer beneath your skin which is above the muscle layer below that.

Thigh and belly have a lot of fat. But, too much fat is a bad thing so at a certain point of gut it's better to go for thigh. You also don't wanna hit any blood vessels or anything, and the thigh has a lot more of those compared to your belly.

Both work, and it depends on how big you are. But sitting down and getting it into your thigh is a bit easier than your belly.