IAM User with AmazonMechanicalTurkFullAccess Permission Policy Unable to Purchase Prepaid HITs on AWS

I am currently facing an issue while trying to use the Mechanical Turk API on AWS. Specifically, I have configured an IAM user with the AmazonMechanicalTurkFullAccess permission policy. However, when attempting to create a new HIT, I receive the following error message:

RequestError: This Requester has insufficient funds in their account to complete this transaction. Please visit ttps://requester.mturk.com/prepayments/new to purchase Prepaid HITs. (1680098291005)

Upon visiting the page to purchase Prepaid HITs, I encountered the following message:

Your account is configured to pay for HITs using AWS Billing. You are not permitted to purchase Prepaid HITs at this time.

Furthermore, under the billing details on the same page, I received the following message:

Your account is configured to pay using AWS billing.

I have also attempted to use the root user access token, but unfortunately, it still returns the same error.

I would greatly appreciate any guidance or assistance in resolving this issue. Thank you in advance for your kind attention and support. Best regards, Aviv Atedgi.