Once your customers start buying your NFTs, they will receive the Preview Asset and the correspondent preview metadata.
When you decide to reveal your collection, the platform will deliver the final NFTs and metadata to your customers.
Once you hit the Reveal button, a popup from your MetaMask extension will emerge and you'll have to pay the gas to process the revelation.
When paying the gas fee, you are paying the network to process your transaction.
The amount you have to pay depends on factors that aren't handled by KoalaMint and are directly correlated with the network you are using to launch your collection (Ethereum/Polygon).
This process could take from minutes to hours, depending on the number of NFTs your collection has.
You don't have to be waiting for this process to finish, you can check the 'Notify me by email when this process is finished' and the platform will automatically send you an email when it's done.
Important: after this process is finished, please ask your customers to refresh the metadata from OpenSea to see the updated asset and metadata of their NFTs.