On Amazon Mechanical Turk (MTurk), do I have to pay extra to extend a batch of HIT?

The error message is due to a very old problem that already existed in the Amazon system.

The extension of the lot does not cost extra money, but to do this, your account must have a balance greater than or equal to the total cost of the lot.

Once you have added money to your account and extended the lot, you can request a refund to recover the balance from the account.

If you plan to use MTurk in the future, you can also leave your account balance and use it to pay for future orders.