Architect Data Action 403 on Lambda invoke - IAM role config

Architect & Flows
1

Need some help troubleshooting why the Architect Data Action keeps throwing a 403 when it hits the Lambda invoke endpoint. i’ve attached the role ARN to the external account and the trust policy looks right, but it’s bouncing back with "errorMessage": "User: arn:aws:sts::123456789:assumed-role/GenesysLambdaRole is not authorized to perform: lambda:InvokeFunction".

the Data Action JSON is pretty basic, just a POST to https://lambda.us-east-1.amazonaws.com/2015-03-31/function/arn:aws:lambda:us-east-1:123456789:function:gc-processor/invocations with the standard auth headers. something’s definitely off with the cross-account execution role setup.

2

The easiest way to fix this is to ensure the GenesysLambdaRole trust policy explicitly allows sts:AssumeRole for genesyscloud.amazonaws.com, not just the external account. check that the Lambda resource policy also grants lambda:InvokeFunction to that specific role ARN.

3

the Data Action JSON is pretty basic, just a POST to https://lambda.us-east-1.amazonaws.com/2015-03-31/f

You need to attach the lambda:InvokeFunction policy to the role assumed by Genesys, not just the trust relationship. As noted above the trust policy, but you’re missing the actual permissions. here’s the JSON you need to attach to GenesysLambdaRole:

{
 "Version": "2012-10-17",
 "Statement": [
 {
 "Effect": "Allow",
 "Action": "lambda:InvokeFunction",
 "Resource": "arn:aws:lambda:us-east-1:123456789:function:YourFunctionName"
 }
 ]
}

the 403 happens because the assumed role has no permissions to execute the function. trust policy gets you in the door, permissions let you do work.

1 Like
4

the IAM policy is definitely the missing piece here. the trust policy just says “who” can assume the role, but the inline policy says “what” they can do once assumed. if you only set the trust policy, Genesys can get the credentials, but AWS immediately rejects the actual Lambda call because the role itself doesn’t have permission to invoke functions.

you need to attach a policy like this to GenesysLambdaRole:

{
 "Version": "2012-10-17",
 "Statement": [
 {
 "Effect": "Allow",
 "Action": [
 "lambda:InvokeFunction"
 ],
 "Resource": "arn:aws:lambda:us-east-1:123456789:function:YourFunctionName"
 }
 ]
}

also, watch out for the region in the ARN. if your Lambda is in us-west-2 but your Data Action points to us-east-1, you’ll get a 403 or a 404 depending on how AWS resolves the cross-region call. the Data Action URL must match the Lambda’s region exactly.

another thing that trips people up is the external account configuration in Genesys. make sure the external account is set to “AWS” and you’re passing the correct Access Key and Secret Key. if you’re using IAM roles for service accounts (IRSA) or something similar, the signature might fail silently or throw a 403. for a simple Data Action, static keys in the external account usually work best until you get the flow stable.

i’ve also seen cases where the Lambda function itself has a resource policy that denies access from specific principals. double-check the Lambda’s resource-based policy in the AWS console. it should look something like this:

{
 "Version": "2015-03-31",
 "Id": "default",
 "Statement": [
 {
 "Sid": "AllowGenesysInvoke",
 "Effect": "Allow",
 "Principal": {
 "AWS": "arn:aws:iam::123456789:role/GenesysLambdaRole"
 },
 "Action": "lambda:InvokeFunction",
 "Resource": "*"
 }
 ]
}

if both the role policy and the Lambda resource policy are aligned, the 403 should disappear. check the CloudWatch logs for the Lambda function too, sometimes the error message in Genesys is misleading and the real issue is a timeout or a malformed request body.

3 Likes
5

The trust policy is often where the issue lies. Many admins configure the role to allow sts:AssumeRole for a specific AWS account ID, but Genesys Cloud uses a service principal. If the Principal block in the trust relationship does not explicitly list genesyscloud.amazonaws.com, the assume role call fails before the permissions are even checked.

We have seen this frequently in our multi-site setup. The external account must have the correct role ARN, but the role itself must trust the Genesys service. Here is the exact JSON structure for the trust policy. It must be attached to the GenesysLambdaRole.

{
 "Version": "2012-10-17",
 "Statement": [
 {
 "Effect": "Allow",
 "Principal": {
 "Service": "genesyscloud.amazonaws.com"
 },
 "Action": "sts:AssumeRole",
 "Condition": {}
 }
 ]
}

Also, check the timezone handling. Our environment is in Europe/Berlin, but the Lambda is in us-east-1. If the Data Action sends timestamps without explicit UTC formatting, AWS might reject the request or the Lambda might process the wrong time window. Ensure the payload sends ISO 8601 strings with the Z suffix. For example, 2023-10-27T14:30:00Z.

We also noticed that if the Lambda resource policy is too restrictive, it blocks the invocation. The resource policy on the Lambda function must allow the specific role ARN to invoke it. It is not enough for the role to have the permission. The Lambda function must also grant the permission. This is a common oversight.

Check the CloudWatch logs for the Lambda. If the error is User is not authorized, it is the role policy. If it is Resource policy denies, it is the Lambda function policy. Both must align. We spent two days on this because we only fixed the role policy. The Lambda resource policy was still using an old ARN. Update both and retry the Data Action.

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