On mainnet those vending machines are not instant and need to wait up to 3 confirmations of the TX.
3 confirmations is unnecessary for the amounts being spent at a vending machine. No one is going to attempt to reverse 3 blocks worth of block subsidy and fees for the price of a one dollar chocolate bar. 1 confirmation would be sufficient, but Lightning would be better.
Without confirmations all UXTOs can be double spending with FullRBF feature.
No. As I said above, without confirmation all UTXOs could
always be double spent. Full RBF just standardizes the process.
Let me change it, I used to use imgur and always used lower size images, but sadly that hosting is not longer working on bitcointalk.
Just include a height or width parameter in the img code. For example:
[img width=800]https://www.talkimg.com/images/2023/09/03/mSaMD.jpeg[/img]