Why do some members of my team see a “Diamond Bonanza” showing 500 diamonds for $19.99?

Sale offers vary from person to person. Some are priced differently because of the platform used and country they live, some are based on the player's past history of purchases, some have no explanation whatsoever. If you have an existing offer, you may just need to wait until this offer is over, since only one offer is available at a time. Some people never get these offers, while other get all the offers, while most get most of the offers.