Importmodule error for 'serverless-http'?

Hey folks,
First time dealing with serverless here. Have successfully deployed using serverless deploy after following the guide to migrating an existing express app over to serverless. But aws lambda keeps throwing an error:
“errorType”: “Runtime.ImportModuleError”,
“errorMessage”: “Error: Cannot find module ‘serverless-http’\nRequire stack:\n- /var/task/app.js\n- /var/runtime/UserFunction.js\n- /var/runtime/index.js”,

So I’m confused. What am I doing wrong? The guide to converting an existing express app didn’t say we’d need to create an AWS Lambda Layer, but since it seems like Lambda can’t find the serverless-http module, does it mean that creating a layer is the fix?