The 5x Bonus RP can be bought from Wondrous Bazaar during Bonus Refinement Point Event.
Tooltip
5x Bonus RP
Increases the amount of Refinement Points earned during the Bonus Refinement Point Event to 5 times the normal amount. This boost will last until the end of the event and does not increase the maximum RP that can be earned during the event.
No Level Requirement
Cannot sell