I have a batch of HITs on Amazon Mturk that aren't quite done yet. They're about to expire and I want to extend the time (not the number of HITs) so that the batch can finish.
However, when I click the "Extend this batch" button, Amazon gives me this error message:
Your account does not have sufficient funds to extend these HITs. Click here to fund your account.
I was under the impression that the cost was based on the number of assignments and not the length of time. Is that not the case? Can I not extend the batch for free?