policies

I am a software developer who is currently working on an AWS project. While trying to create a new role, I keep facing the same problem. Whenever I try to create a new IAM role with a certain policy document, AWS CloudFormation throws an error message stating that the ‘createRole’ action has a prohibited field.
Here is the code I am using to create the role:

Resources:
myRole:
Type: 'AWS::IAM::Role'
Properties:
RoleName: 'myRole'
AssumeRolePolicyDocument:
Statement:
- Effect: Allow
Principal:
Service:
- ec2.amazonaws.com
Action:
- 'sts:AssumeRole'
ManagedPolicyArns:
- arn:aws:iam::aws:policy/AmazonS3FullAccess
- arn:aws:iam::aws:policy/AmazonEC2FullAccess
Policies:
- PolicyName: 'myPolicy'
PolicyDocument:
Statement:
- Effect: Allow
Action: ['ec2:StartInstances']
Resource: ['arn:aws:ec2:*:*:instance/*']

What could be causing this error message? I have tried various ways to change the policy document, but I still get the same error. Is there something wrong with my IAM role creation syntax? Any help would be much appreciated.