Can I transfer money to Apple Pay from a Visa gift card ?

Visa gift cards are not redeemable for cash, which is what Apple Cash is. And Apple Pay is a way to use credit or debit cards for purchases. You can try to add the gift card to Apple Pay, but it will probably refuse to let you. But give it a try; nothing to lose→Set up Apple Pay - Apple Support

Pay with your default card on an iPhone with Face ID

1. Double-click the side button.
2. When your default card appears, glance at iPhone to authenticate with Face ID, or enter your passcode.
3. Position the top of iPhone within a few centimeters of the contactless reader until you see Done and a checkmark on the screen.

Use Apple Pay for contactless payments on iPhone

So I used a 25 dollar gift card and I tried to buy something in an app and it seems like apple took 12 dollars leaving me with only 13? Why did you guys take 12 dollars I didn’t get anything in reward.

We guys (the other users in this user-to-user forum) didn’t take anything.