I want to create an IAM user that acquires the Assumerole. In the case of the uat environment, I want it to acquire the Assumerole for the 123451234512 account, and in the case of stg, I want it to acquire the Assumerole for the 123451234513 account, using a specific AccountId depending on the environment.
When I write the code as below and execute it in CloudFormation, I get a “Syntax errors in policy” error.

AWSTemplateFormatVersion: '2010-09-09'
Description: Create test User
Parameters:
  NetworkEnvironment:
    Description: test
    Type: String
    Default: uat
    AllowedValues:
      - uat
      - stg
      - prd

Mappings:
  AccountMap:
    uat:
      AccountId: "123451234512"
    stg:
      AccountId: "123451234513"
    prd:
      AccountId: "123451234514"

Resources:
  User01:
    Type: AWS::IAM::User
    DeletionPolicy: Retain
    Properties:
      Path: /
      UserName: !Sub ${NetworkEnvironment}-test-user
      Tags:
        - Key: Name
          Value: !Sub ${NetworkEnvironment}-asd
        - Key: Environment
          Value: !Sub ${NetworkEnvironment}

  Policy01:
    Type: AWS::IAM::Policy
    DeletionPolicy: Retain
    Properties:
      PolicyName: !Sub ${NetworkEnvironment}-test-policy
      PolicyDocument:
        Version: '2012-10-17'
        Statement:
          - Effect: Allow
            Action:
              - logs:PutLogEvents
              - logs:GetLogEvents
            Resource: '*'
      Users:
        - !Ref User01

  Policy02:
    Type: AWS::IAM::Policy
    DeletionPolicy: Retain
    Properties:
      PolicyName: !Sub ${NetworkEnvironment}-test-assume-role
      PolicyDocument:
        Version: '2012-10-17'
        Statement:
          - Effect: Allow
            Action: sts:AssumeRole
            Resource: !Sub arn:aws:iam::${!FindInMap [AccountMap, !Ref NetworkEnvironment, AccountId]}:role/testbucket1209
      Users:
        - !Ref User01

Can somebody help me on this? Thanks!