Why doesn't Apple Pay on my Apple Watch work on all vending machines?

So I recently got the Apple Watch SE 2 and I have Apple Pay on it and so I use it at the vending machines they have at my work and both of the vending machines have contactless payment with Apple Pay and so when I use Apple Pay on my Apple Watch, it works with one vending machine but when I try to get something from the other vending machine it didn’t recognize Apple Pay on my Apple Watch and so I pulled out my iPhone and then the vending machine recognize it and so I’m confused and wondering is it my Apple Watch malfunctioning or???

[Re-Titled by Moderator]