AWS Lambda (Python) - FCM Integration with Default VPC is not working

I have followed below link and integrated FCM into AWS Lambda (Python) function.

https://github.com/olucurious/PyFCM.

Its works fine with no VPC configured. But when I integrate with Lambda method to query RDS using default VPC configured, its not working. Always am getting timeout in FCM send message.

Kindly share if you have any thoughts.