While he acknowledged doing cocaine with Liam Payne, the waiter refused to be paid.

A waiter prosecutors want to charge in connection with Liam Payne’s death admits he used cocaine with the singer … but insists he didn’t get paid and is NOT a drug dealer.

Braian Paiz told us in our upcoming documentary “TMZ Investigates: Liam Payne: Who’s to Blame?”

— airing Monday night at 8 PM ET on FOX — he partied with Liam in the singer’s Buenos Aires Hotel room.

Paiz says they drank whiskey and used the cocaine he brought to the hotel.

He says they did it on 2 occasions … the second just 2 days before Liam’s fatal fall from the hotel balcony.

Braian says he saw drugs scattered everywhere … along with the Dove soap box and tin foil widely seen in photos taken after Liam’s death.

Braian says he never accepted money from the singer … and claims he even turned down Payne’s Rolex watch when the star offered it as payment.

There is one gift he did take from Liam, Paiz says … watch the clip to hear what keepsake he received.

Paiz is one of five men prosecutors are going after in connection with Liam’s death.

We also interviewed Liam’s close friend Roger Nores— whom prosecutors accuse of abandonment and supplying Liam with drugs — and eyewitness Bret Watson … who saw Liam fall to his death.