Rihanna: After I Work ... Strippers Go to Work, Work, Work

Rihanna hopped off her Houston concert stage and beelined it to the main stage at a strip club ... where she was just a spectator -- but a well paying one.

RiRi and Travis Scott -- her opening act -- hit up V Live early Monday morning. Armed with stacks, they rolled in around 3:30 AM and stayed for 2 hours.

We're told she was very generous with about $15k worth of bills ... and you can tell from this video -- the crowd, not just the strippers, ate it up. Though Rihanna seemed to enjoy it the most.