Why do I keep getting a Cancel Purchase warning when I try to equip my Sidekick in Fortnite Creative Islands?

Players may receive the following Cancel Purchase warning in-game when they try to equip a Sidekick for the first time:

INFO ABOUT CANCEL PURCHASE

You are matchmaking or in a game right now. If you equip or use this purchase during gameplay you will lose the ability to cancel purchase on this purchase.

For more information see fn.gg/cancelpurchase

This error happens when a player has multiple variations of the same sidekick. To bypass this error, players can edit and equip all variations of the same sidekick before going into a Creative Island. Please note that doing so will disable the Cancel Purchase option for that purchase.