I had this error occur when trying to buy the Headless Horseman bundle in the Halloween Spotlight event hub:
Expected behavior
I would expect the error to say something like “Cannot buy this large of an amount with one purchase of robux, please leave the experience and go to the robux page to buy more”. Obviously not worded the best, but it gives the idea of a better error message.
Alternatively the error popup should allow for opening up a webview that shows the purchase robux page, with a choice saying “Open Robux Page”. Which would be an overall better UX than just telling people to leave the game to buy robux.