Only issue i am facing is that when i run my API GW Endpoint with query params, it does not invoke lambda function.
Although locally everything is working + when i manually test my API on API GW with params it works there.
Check the API Gateway config in the console and make sure that the integration with lambda is there. You should be able to invoke that integration with the lambda directly with a test event. You can also enable access logging on the APIG itself to see what is happening when the route is called.
Also that article is 2 years old, so it’s a bit outdated. It uses APIG v1’s HTTP API for example, which is more complicated to set up and use than APIG v2’s REST API.
If you’re just starting out today I’d suggest using CDK instead of YAML-based CloudFormation - and the best framework out there today for CDK is SST imo: https://serverless-stack.com/examples/index.html