AWS Fargate can't resolve Private DNS Route 53

I have a Cloudformation that creates a AWS Fargate on ECS Cluster, in this way:

  TaskDefinition:
    Type: 'AWS::ECS::TaskDefinition'
    Properties:
      RequiresCompatibilities:
        - FARGATE
      Cpu: !Ref ContainerCpu
      Memory: !Ref ContainerMemory
      ExecutionRoleArn: !Ref ExecutionRole
      TaskRoleArn: !Ref ExecutionRole
      ContainerDefinitions:
        - Name: !Sub ${ContainerName}
          Image: 'image-url-here'
          Essential: true
          HealthCheck:
            Command: ["CMD-SHELL", "test -f hc.log"]
          LogConfiguration:
            LogDriver: awslogs
            Options:
              awslogs-region: !Sub '${AWS::Region}'
              awslogs-group: !Sub '${FeatureName}-${MicroServiceName}'
              awslogs-stream-prefix: !Ref MicroServiceName
      Family: !Sub 'family-${FeatureName}-${MicroServiceName}'
      NetworkMode: awsvpc
    DependsOn: CloudWatchLogGroup
    
  ExecutionRole:
    Type: AWS::IAM::Role
    Properties:
      RoleName: !Join ['', [!Ref MicroServiceName, ExecutionRole]]
      AssumeRolePolicyDocument:
        Statement:
          - Effect: Allow
            Principal:
              Service: ecs-tasks.amazonaws.com
            Action: 'sts:AssumeRole'
      ManagedPolicyArns:
        - 'arn:aws:iam::aws:policy/service-role/AmazonECSTaskExecutionRolePolicy'
    
    

My ECS Task Fargate need to access a API that is running in a EC2 , so I created a DNS Private Hosted Zone with the following address: api.localaccount. But when I try to access this API from my Fargate i got the following error:

System.Net.Http.HttpRequestException: Name or service not known

I know that this error is because my AWS Fargate can't resolve DNS, but I don't know why. If I access this same DNS (api.localaccount) from EC2 everything works fine, so I think my DNS Route 53 is ok.

Based on the comments.

The issue was due to the use of a wrong link in the application. Thus, it was application-level problem, not ECS Farage issue.