You will be notified with a word "success" once the purchase was consumated. There must be a 24 hour time that will show underneath the 24hrs stamina potion. If there is non and when you play stage games, the stamina is still decreased then you encountered some glitch in the purchase.
My friend had a problem like this once and told me his solution is to use the 24hrs stamina ONLY after turning off the wifi or data on his phone and restarting the game to avoid the glitch (use offline mode). This problem never happened to me that a purchase didn't worked so I could not verify. You could try this steps if it works for you 👍