Accessing Resources Across Accounts

Serverless Framework
,
1

Hi Folks,

I am trying to set up access to resources across AWS accounts using serverless. I am using serverless to deploy resources in a child account and need access to services in the parent account. For testing purposes I have created a role in the parent account that has the AdministratorAccess IAM policy attached to it. The child serverless.yml file looks like this:
service: test-service

frameworkVersion: '2'

custom:
  stage: dev
  crossAccountAccessRoleName: ${self:service}-${self:custom.stage}-crossAccountAccessRole

provider:
  name: aws
  runtime: nodejs12.x

resources:
  Resources:
    crossAccountAccessRole:
      Type: AWS::IAM::Role
      Properties:
        RoleName: ${self:custom.crossAccountAccessRoleName}
        AssumeRolePolicyDocument:
          Version: '2012-10-17'
          Statement:
            - Effect: Allow
              Principal:
                Service:
                  - lambda.amazonaws.com
              Action: sts:AssumeRole
        ManagedPolicyArns:
          - arn:aws:iam::aws:policy/service-role/AWSLambdaVPCAccessExecutionRole
        Policies:
          - PolicyName: crossAccountAccessPolicy
            PolicyDocument:
              Version: '2012-10-17'
              Statement:
                - Effect: Allow
                  Action:
                    - logs:CreateLogGroup
                    - logs:CreateLogStream
                    - logs:PutLogEvents
                  Resource:
                    - 'Fn::Join':
                        - ':'
                        - - 'arn:aws:logs'
                          - Ref: 'AWS::Region'
                          - Ref: 'AWS::AccountId'
                          - 'log-group:/aws/lambda/*:*:*'
                - Effect: 'Allow'
                  Action:
                    - 's3:PutObject'
                  Resource:
                    Fn::Join:
                      - ''
                      - - 'arn:aws:s3:::'
                        - 'Ref': 'ServerlessDeploymentBucket'

functions:
  crossAccountFunc:
    handler: apiCrossAccountFunc.handler
    role: crossAccountAccessRole

After creating the new role using serverless I took the ARN of the newly created role and added it as a trusted relationship on the parent’s role. The crossAccountFunc calls listBucket on a named bucket that is located in the parent account, however fails as its unauthorised. Any ideas?