External macro implementation type could not be found

Hi, would someone mind helping me with my first macro? I keep getting the error mentioned in the title. I tried to create a minimal example of this as follows:

  1. Created a CLI project with XCode.
  2. Created a macro package with XCode, and added it to my project. I haven't changed the macro package at all from its default state, so it only has the stringify example that comes with it.

At this point, my directory structure is as follows:

MyProject

  • MyStringify (name I gave to the macro package; I haven't changed anything in this directory)
  • MyProject
    • main.swift

In main.swift, I have:

import Foundation
import MyStringify
var x = #stringify(63)

This throws the error: "External macro implementation type 'MyStringifyMacros.StringifyMacro' could not be found for macro 'stringify'"

I know that it's able to import MyStringify and able to recognize the stringify macro. But apparently it can't find the implementation. It's as if this block from the implementation is being ignored.

@main
struct MyStringifyPlugin: CompilerPlugin {
    let providingMacros: [Macro.Type] = [
        StringifyMacro.self,
    ]
}

If anyone has suggestions for what I'm missing, I'd appreciate it. Maybe there needs to be a package file at the top level? But there wasn't one in the video tutorial I watched (https://www.youtube.com/watch?v=OZQE8tMuCdw&t=906s).

Thank you!