Status (Feb 23 08:30 GMT): We have now removed the offer for the time being.
There is a known issue with the new "Tranquil Treasure" offer causing the gem price missing and the offer being unpurchasable. We are currently investigating this issue.
We recommend not to tap the purchase button as this will cause the purchase being stuck and shop not available. Restarting the app will resolve this issue. Please note that no gems are spent on this purchase.
We have now disabled the offer, but we'll be reintroducing it soon!
Our apologies for the inconvenience!