Intereses translates to "interest," as in the fee you pay on a loan. This word is the key to the song's clever central metaphor and title, "El Préstamo" (The Loan).
Maluma sings that he only lent his heart, he didn't give it away. He cheekily warns his lover, "Ojalá no olvides de pagar los intereses" (I hope you don't forget to pay the interest), implying his affection isn't free and requires her continued effort and attention.
Have you ever felt like you've been hurt so badly in past relationships that you can't give your heart away again? That's the whole idea behind this track from Colombian superstar Maluma. He uses the metaphor of a loan to talk about love, and it's a pretty bold move. He tells a woman straight up that his love isn't a gift. Instead, he says, "Yo no lo di, yo no lo di, yo lo presté" (I didn't give it, I didn't give it, I lent it).
He's not trying to be romantic here; he's being brutally honest about where he's at. He explains that his past has made him this way, saying "En el juego del amor mucho he perdido" (In the game of love I have lost a lot). He's basically telling her that he's happy to be with her, but she needs to know the deal: his heart is only on loan, and he's going to need it back to use "Contigo y con otras más" (With you and with other women). It's a classic reggaeton mix of confidence and vulnerability, all wrapped up in a warning not to get too attached.