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Error: make sure your module has a default export of a service.

If you get the following error while building your Medusa application:

Terminal

...doesn't seem to have a main service exported -- make sure your module has a default export of a service

Why this Error Occurred#

This error occurs when you set the resolve path of a module provider to point directly to a service file instead of the module directory.

For example, if you set the resolve path to ./src/modules/slack/service:

medusa-config.ts
module.exports = defineConfig({
  // ...
  modules: [
    {
      resolve: "@medusajs/medusa/notification",
      options: {
        providers: [
          {
            resolve: "./src/modules/slack/service",
            id: "slack",
            options: {
              channels: ["slack"],
              webhook_url: process.env.SLACK_WEBHOOK_URL,
              admin_url: process.env.SLACK_ADMIN_URL,
            },
          },
        ],
      },
    },
  ],
})

You'll get the error because the resolve path is pointing to the service file of the module provider, while it should point to the module directory.

How to Fix it#

To fix the error, set the resolve path to point to the module directory instead of the service file. For example:

medusa-config.ts
module.exports = defineConfig({
  // ...
  modules: [
    {
      resolve: "@medusajs/medusa/notification",
      options: {
        providers: [
          {
            resolve: "./src/modules/slack",
            id: "slack",
            options: {
              channels: ["slack"],
              webhook_url: process.env.SLACK_WEBHOOK_URL,
              admin_url: process.env.SLACK_ADMIN_URL,
            },
          },
        ],
      },
    },
  ],
})

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