RDS Proxy IAM role unable to retrieve credentials from secret

I am trying to implement a proxy to our Aurora RDS instance, but having difficulty getting the IAM access to work properly. We have a microservice in an ECS container that is attempting to access the database. The steps I've followed so far:

• Created a secret containing the DB credentials
• Created the proxy with the following config options:
  • Engine compatibility: MySQL
  • Require TLS - enabled
  • Idle timeout: 20 minutes
  • Secret - Selected DB credential secret
  • IAM Role - Chose to create new role
  • IAM Authentication - Required
• Modified the policy of the proxy IAM role as per the details on this page.
• Enabled enhanced logging

When issuing GET requests to the microservice, I see the following in the CloudWatch logs:

Credentials couldn't be retrieved. The IAM role "arn:our-proxy-role" is not authorized to read the AWS Secrets Manager secret with the ARN "arn:our-db-credential-secret"

Another interesting wrinkle to all of this: I pulled up the policy simulator, selecting the RDS proxy role and all of the actions under the Secrets Manager service, and all actions show up as being allowed.

I would sincerely appreciate any kind of guidance to indicate what I'm missing here.

arn:our-proxy-role

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Action": [
                "rds-db:connect"
            ],
            "Resource": [
                "arn:aws:rds:us-east-1:ACCOUNT:dbuser:*/*"
            ]
        },
        {
            "Sid": "VisualEditor0",
            "Effect": "Allow",
            "Action": [
                "secretsmanager:GetRandomPassword",
                "secretsmanager:CreateSecret",
                "secretsmanager:ListSecrets"
            ],
            "Resource": "*"
        },
        {
            "Sid": "VisualEditor1",
            "Effect": "Allow",
            "Action": "secretsmanager:*",
            "Resource": [
                "arn:aws:our-db-credential-secret"
            ]
        },
        {
            "Sid": "GetSecretValue",
            "Action": [
                "secretsmanager:GetSecretValue"
            ],
            "Effect": "Allow",
            "Resource": [
                "arn:aws:our-db-credential-secret"
            ]
        },
        {
            "Sid": "DecryptSecretValue",
            "Action": [
                "kms:Decrypt"
            ],
            "Effect": "Allow",
            "Resource": [
                "arn:aws:kms:us-east-1:ACCOUNT:key/our-db-cluster"
            ],
            "Condition": {
                "StringEquals": {
                    "kms:ViaService": "secretsmanager.us-east-1.amazonaws.com"
                }
            }
        }
    ]
}

The issue was related to security groups. I needed to specify an additional inbound rule to allow incoming traffic from itself so as to facilitate communication between resources that are part of the same security group.