Greedo talks as though Jabba has already given up on Han and has already put a significant price on his head.
Shortly after, Jabba and Han talk as though Greedo is just Jabba’s lackey and Jabba is looking for Han to pay up, threatening only then to put a bounty on his head.
I agree with all this. Of course, there are ways to rationalize it. Perhaps Greedo is exaggerating Jabba’s anger level in order to trick Han into handing over all the money he owes Jabba - so that Greedo can pocket it, perhaps after killing Han. Greedo tells Han “If you give [the money] to me, I might forget I found you.”
But I agree the whole thing is still very weird - the two scenes are redundant, and suggest entirely different threat levels from Jabba. But early drafts of Star Wars indicate these two scenes were NOT supposed to be mutually exclusive. Both the Greedo scene and the Jabba scene appear together in early drafts, indicating Lucas really did originally want to have both scenes. The best explanation is that Greedo was trying to pocket the money owed to Jabba from Han. His name is “Greedo” after all.