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# Refund Mechanism for Expired Deposits
Given that the set of validators in the TON network changes every 18 hours, deposit addresses associated with these validators also ”expire” after each rotation. This means that if a user initiates a Bitcoin transaction and the corresponding tgBTC has not yet been minted before the validator set changes, the deposit address will no longer be valid, and the transaction cannot be completed. To address this situation, the TON Teleport BTC system includes a refund mechanism that allows users to reclaim their BTC in case of expired deposit addresses.
When generating a deposit address, the user has the option to provide a Bitcoin public key, which will be used to construct an OP CSV script (CheckSequenceVerify) within the Bitcoin transaction. This script allows the user to reclaim their deposited BTC after a specified timeout period (typically two weeks) if the peg-in operation is not completed within that time. The refund process differs depending on the level of security chosen by the user:
The refund process is designed to be flexible and secure, allowing users to choose the level of protection that best suits their needs while maintaining the trustless nature of the TON Teleport BTC system.
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