cannot create aws lamda function due to some cryptic error message

From the Lambda@Edge IAM Role documentation:

You must create an IAM role that can be assumed by the service principals lambda.amazonaws.com and edgelambda.amazonaws.com. This role is assumed by the service principals when they execute your function. For more information, see Creating the Roles and Attaching the Policies (Console) in the topic "AWS Managed Policies for Job Functions" in the IAM User Guide.

You add this role under the Trust Relationship tab in IAM (do not add it under the Permissions tab).

Here's an example role trust policy:

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

Note : If you're doing this via the AWS Console then you have to refresh the browser after you update your IAM Role Credits: from comments @AJB

This video https://www.youtube.com/watch?v=BZzEXVkVOM8 explains the issue.

Issue: 5:39

And the resolution 6:33