Including the file extension serves the file. Actually I was able to resolve this by adding routes to the configuration. Here’s the updated configuration that works:
vercel.json
{
"version": 2,
"builds": [{ "src": "api/*.js", "use": "@vercel/node" }],
"routes": [
{ "src": "^/api/hello$", "dest": "/api/hello.js" },
{ "src": "^/api/test$", "dest": "/api/test.js" },
{ "src": "^/api/.*$", "dest": "/api/index.js" }
]
}