NoCredentialsError on attempted write to SQS from ECS (Fargate)

I have been struggling for hours to push a message to SQS from a running ECS container. I have done the following:

• Added all available SQS policies to ECS task execution role
• Added access policy to SQS giving full rights to ECS task execution role
• Added VPC endpoint allowing everything and anything

Yet when my container application attempts to post a message to a queue (tested and working) boto3 raises NoCredentialsError. From what I read, setting up IAM roles should resolve this but it is not working for me. I have given overly broad access in all of these cases in an attempt to just get something to work. Are there any other steps I need to take to allow my ECS container to interact with SQS?

Here are the configurations as mentioned above:

IAM policy attached to ecsTaskExecutionRole:

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "VisualEditor0",
            "Effect": "Allow",
            "Action": [
                "sqs:DeleteMessage",
                "sqs:GetQueueUrl",
                "sqs:ChangeMessageVisibility",
                "sqs:ReceiveMessage",
                "sqs:SendMessage",
                "sqs:GetQueueAttributes",
                "sqs:ListQueueTags",
                "sqs:ListDeadLetterSourceQueues",
                "sqs:PurgeQueue",
                "sqs:DeleteQueue",
                "sqs:CreateQueue",
                "sqs:SetQueueAttributes"
            ],
            "Resource": "arn:aws:sqs:*:<account>:*"
        }
    ]
}

SQS access policy (NOTE: initially tried setting service instead of principal):

{
  "Version": "2012-10-17",
  "Id": "__default_policy_ID",
  "Statement": [
    {
      "Sid": "__owner_statement",
      "Effect": "Allow",
      "Principal": {
        "AWS": "arn:aws:iam::<account>:role/ecsTaskExecutionRole"
      },
      "Action": "SQS:*",
      "Resource": "arn:aws:sqs:us-east-1:<account>:messages"
    }
  ]
}

VPC Endpoint Policy:

{
	"Statement": [
		{
			"Action": "*",
			"Effect": "Allow",
			"Principal": "*",
			"Resource": "*"
		}
	]
}

The VPC endpoint is attached to the all subnets in the VPC (I only have one in the account).

Why am I still getting NoCredentialsError in ECS when attempting to write to the queue? Is this even possible?