But unfortunately when deployed, it returned this error: error decoding lambda response: json: cannot unmarshal string into Go struct field .multiValueHeaders of type []interface {}
I don’t think you need Netlify Lamda. When you build a website with functions, Netlify automatically builds the functions without you having to specify anything else apart from the functions directory in netlify.toml.
In any case, if you can provide a repo to test, that would be great.