Tub leaking at the supply line
You (or someone) has used pipe thread couplings to adapt the 3/4" faucet inlet to those supply lines, this is not (IMO) the best practice.

Stainless braided flex supply lines with a 3/4" connector are available, specifically for your application. Decorative covers (generally called "shrouds") are also available with which to hide the supply lines if you don't like their look.



Specifications:
Overall Length: 37"
Rough-in Connection: 1/2"
Faucet Connection: 3/4"
Braided Stainless Steel