Help in setting up a Lambda in Account A to be Invoked and use a Custom Resource Service Token in Account B Using CloudFormation

Pls help I have a Lambda function in Account A that I need to use as a service token for a custom resource in Account B.

Pleas help with a Cloudformation Setup

Below is my Setup

Account A Resource

Resources:
  MyLambdaFunction:
    Type: AWS::Lambda::Function
    Properties:
      FunctionName: MyLambdaFunction
      Handler: index.handler
      Role: arn:aws:iam::<Account A ID>:role/LambdaExecutionRole
      Code:
        S3Bucket: my-bucket
        S3Key: my-lambda-code.zip
      Runtime: python3.8
      Timeout: 60

Account B Resource

Resources:
  MyCustomResource:
    Type: "Custom::MyCustomResource"
    Properties:
      ServiceToken: "arn:aws:lambda:AccountA:region:function:MyLambdaFunction"