Wiktionary
sweeten the pot
vb. 1 (context idiomatic English) To increase a wager. 2 (context idiomatic English) To make something more desirable.
Usage examples of "sweeten the pot".
But I figured that it was worthwhile complaining about it, since the baron might sweeten the pot a bit to get me there.
Perhaps Hastings enticed him with a barrister's position for Francis to sweeten the pot.