Puesto pa' ti is a popular slang phrase you'll hear a lot in modern reggaetón. It's a shortened way of saying "estoy puesto para ti".
While puesto can mean "put" or "placed", in this context it means you are completely dedicated, focused on, or "down for" someone. It's a strong declaration of loyalty and availability.
In the song, Bad Bunny uses this phrase as his main message to his partner, telling her that despite what others say, he is 100% there for her.
Bad Bunny and Bryant Myers are trying to prove their loyalty to a girl who keeps hearing rumors that they are unfaithful. The title phrase "puesto pa' ti" is essential Puerto Rican slang that means being completely devoted, focused, and ready for someone. In the chorus, they beg her not to listen to gossip, insisting that they ignore everyone else: "Le picheo a to' estas putas por ti" (I ignore all these women for you). Here, the verb "pichear" comes from baseball (to pitch), but in everyday Puerto Rican street talk, it means to ignore, brush off, or give someone the cold shoulder.
The lyrics mix raw physical attraction with surprisingly intense romantic promises. Bad Bunny admits he is far from perfect ("Yo no soy un hombre perfecto" [I am not a perfect man]), but offers to leave behind weed and pills ("el pasto y las perco" [weed and Percocet]) to heal her old heartbreak. Bryant Myers takes things even further, showering her with luxury gifts ("to' lo que te compro es Gucci o Chanel" [everything I buy you is Gucci or Chanel]) and making dark, funny threats toward her ex: "Dile a tu ex que no se pase de listo / O le mando un pasaje pa' allá arriba con Jesucristo" (Tell your ex not to act smart, or I'll send him a one-way ticket up there to Jesus Christ). It is a blunt, explicit track about clearing out contacts and resisting temptations just to keep one special person by their side.