An RTP range means the same slot exists in several certified versions with different RTP settings, and the casino chooses which to offer. The game looks and plays the same; only the long-run payback differs.
Studios create these versions so operators can choose their margin. The maths is usually adjusted by small changes to reel strips or feature odds, so the difference is invisible on screen. Over a large amount of play, though, a version a few points lower costs noticeably more. Illustrative example: on £1,000 staked, a 96% version has an expected loss of £40 and a 94% version £60.
In Great Britain the game must show the RTP of the version you are actually playing, normally in the help or paytable screen. It is worth checking there rather than relying on a figure from a review, which may describe a different version. Our game pages list the published figures from data.