When purchasing Bitcoin from Coinbase using ACH transfer, the purchase amount is limited to the current value of your holdings on Coinbase. Since ACH transfers typically take a few days to clear, Coinbase places a hold on your current assets as collateral and then transfers the Bitcoin immediately. Once the ACH transaction clears, the hold is released. To bypass this limit, consider using a different payment method or purchasing Bitcoin directly on Coinbase and then transferring it to Bitkey once it becomes available.