AWS SAM template - trouble referencing my API inside lambda function - circular dependency.

I have an AWS SAM app template as follows...

Basically the app has 2 lambdas and an API.

Let's say lambda1 has a get, post, put and delete function for path /hello in the api. And lambda2 has a get, post, put and delete function for path /world in the api.

For POST /world in the API, I want to first call GET /hello, then do something with that data and the payload from POST /world.

I am trying to achieve this by defining an API_ROUTE environment variable for my lambdas in the template file. I can find lots of examples of how to get the API base url as an output from the app. But if I try to reference this output as an environment variable it doesn't work, and if i try to build it with the !Sub function, there's a circular dependency.

How can I achieve this or should I be going about this in a different way?

---
AWSTemplateFormatVersion: '2010-09-09'
Transform: AWS::Serverless-2016-10-31

Globals:
  Function:
    Runtime: python3.9
    Handler: app.lambda_handler
    Timeout: 180
    Environment:
      Variables:
        API_ROUTE: !Ref MyAPI # - doesn't work
        API_ROUTE: !Sub "https://${MyAPI}.execute-api.${AWS::Region}.amazonaws.com/prod/" # - produces circular dependency error

Outputs:
  APIEndpoint:
    Description: "API Prod stage endpoint"
    Value: !Sub "https://${MyAPI}.execute-api.${AWS::Region}.amazonaws.com/prod/"
  
Resources:
  ##### Functions
  Lambda1:
    Type: AWS::Serverless::Function
    Properties:
      CodeUri: lambda1/
  Lambda2:
    Type: AWS::Serverless::Function
    Properties:
      CodeUri: lambda2/
      Policies:
        - AmazonAPIGatewayInvokeFullAccess # in reality i'd make this be more specific
        - Version: '2012-10-17'
  ##### API
  MyAPI:
    Type: AWS::Serverless::Api
    Properties:
      Auth:
        DefaultAuthorizer: None 
      StageName: prod
      DefinitionBody:
        path_to_definition_body
  MyApiInvokeRole:
    Type: "AWS::IAM::Role"
    Properties:
      AssumeRolePolicyDocument:
        Version: "2012-10-17"
        Statement:
          - Effect: "Allow"
            Principal:
              Service: "apigateway.amazonaws.com"
            Action:
              - "sts:AssumeRole"
      Policies:
        - PolicyName: InvokeLambda
          PolicyDocument:
            Statement:
              - Effect: "Allow"
                Action:
                  - lambda:InvokeFunction
                Resource: "*" # in reality i'd make this be more specific