When I try to deploy a session on Mturk, ticking "Use MTurk Sandbox (for development and testing), an MTurkError occurs, saying that to use MTurk API I need an AWS account linked to Amazon MTurk account. In fact, I have an AWS account and my MTurk account is linked to AWS. Does anyone had and solved the same problem? (I add that I have no problems in running sessions on Mturk; the problem is that I cannot test them and see how they appear to workers). Thank you.

Can you log in to your sandbox account on https://requestersandbox.mturk.com/?

You may need to connect your sandbox account to your AWS-Account as well.