Send your first Slack message

Slack needs one thing the other channels do not: an app you create, installed into the workspace you want to post in. Once its bot token is on a profile, a Slack message is the same send as an email.

Prerequisites

A Slack workspace you can install an app into
A published with a Slack channel

The token belongs to the recipient

This is the part that surprises people, and it is worth understanding before you start. Most providers hold one credential on the integration. Slack passes its bot token with each recipient, on to.slack.access_token. Install the Slack integration once, then store a token per user or per customer. That is what makes Slack workable for B2B. One Courier workspace posts into many customers’ Slack workspaces, because each recipient carries the token for the workspace they belong to. A single shared credential could not do that.

Send it

Install the integration and create a Slack app

Add Slack from in Courier.Then create the app on Slack’s side. At api.slack.com/apps, choose Create an App, then From scratch, and pick your workspace.Under OAuth & Permissions, add these Bot Token Scopes:

Scope	Why
`chat:write`	Post messages
`im:write`	Open a direct message channel
`users:read`	Look up workspace members
`users:read.email`	Target a person by their email address

Install the app to the workspace, then copy the Bot User OAuth Token. It starts with xoxb-. has the screenshots for each step.

Put the token and a target on the profile

Store the token alongside how you want to reach the person. Courier accepts three targets, and uses the first one it finds in this order: channel, then user_id, then email. covers profile storage for every channel.

Profile

{
  "profile": {
    "slack": {
      "access_token": "xoxb-your-bot-token",
      "email": "sarah@acme-corp.com"
    }
  }
}

Which target to pick is a real decision rather than a preference:

Target	Reach it with	Worth knowing
`email`	The address they use in Slack	Simplest, and breaks if their Slack email differs from yours
`user_id`	Their Slack member id, `U…`	Stable across email changes, and needs a lookup once
`channel`	A channel id, `C…`	Posts to a room rather than a person

Start with email and move to user_id when a mismatch bites. The users:read.email scope is what makes email targeting work at all.

Send the message

Address the user and route to the Slack provider. Courier reads slack off the profile.

const { requestId } = await client.send.message({
  message: {
    to: { user_id: "user_123" },
    routing: { method: "single", channels: ["slack"] },
    template: "nt_01kx4h2jdafq8bk9aftxak4b40",
  },
});

response = client.send.message(
    message={
        "to": {"user_id": "user_123"},
        "routing": {"method": "single", "channels": ["slack"]},
        "template": "nt_01kx4h2jdafq8bk9aftxak4b40",
    },
)

curl -X POST https://api.courier.com/send \
  -H "Authorization: Bearer $COURIER_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "message": {
      "to": { "user_id": "user_123" },
      "routing": { "method": "single", "channels": ["slack"] },
      "template": "nt_01kx4h2jdafq8bk9aftxak4b40"
    }
  }'

response = courier.send_.message(
  message: {
    to: {user_id: "user_123"},
    routing: {method: "single", channels: ["slack"]},
    template: "nt_01kx4h2jdafq8bk9aftxak4b40"
  }
)

response, err := client.Send.Message(context.TODO(), courier.SendMessageParams{
	Message: courier.SendMessageParamsMessage{
		To: courier.SendMessageParamsMessageToUnion{
			OfUserRecipient: &shared.UserRecipientParam{UserID: courier.String("user_123")},
		},
		Routing: courier.SendMessageParamsMessageRouting{
			Method:   string(shared.MessageRoutingMethodSingle),
			Channels: []shared.MessageRoutingChannelUnionParam{{OfString: courier.String("slack")}},
		},
		Template: courier.String("nt_01kx4h2jdafq8bk9aftxak4b40"),
	},
})

SendMessageParams.Message message = SendMessageParams.Message.builder()
    .to(SendMessageParams.Message.To.ofUserRecipient(
        UserRecipient.builder().userId("user_123").build()))
    .routing(SendMessageParams.Message.Routing.builder()
        .method(SendMessageParams.Message.Routing.Method.SINGLE)
        .channels(List.of(MessageRoutingChannel.ofString("slack")))
        .build())
    .template("nt_01kx4h2jdafq8bk9aftxak4b40")
    .build();

client.send().message(SendMessageParams.builder().message(message).build());

$response = $client->send->message(
  message: [
    'to' => ['user_id' => 'user_123'],
    'routing' => ['method' => 'single', 'channels' => ['slack']],
    'template' => 'nt_01kx4h2jdafq8bk9aftxak4b40',
  ],
);

SendMessageParams parameters = new()
{
    Message = new()
    {
        To = new UserRecipient { UserID = "user_123" },
        Routing = new() { Method = "single", Channels = ["slack"] },
        Template = "nt_01kx4h2jdafq8bk9aftxak4b40",
    },
};

var response = await client.Send.Message(parameters);

courier send message \
  --api-key "$COURIER_API_KEY" \
  --message.to '{"user_id": "user_123"}' \
  --message.routing '{"method": "single", "channels": ["slack"]}' \
  --message.template nt_01kx4h2jdafq8bk9aftxak4b40

With Courier MCP, send my welcome template to user_123 on Slack.

Slack content is built in the template’s Slack block rather than in the send, which is why this call carries a template id and no inline content.

Verify

Check Slack

The message arrives as a direct message from your app, not from a person.

Read the status

Open . The provider response carries Slack’s own error when something fails, which is more specific than the Courier status alone.

Two failures account for most first attempts. not_in_channel means the app is not in the channel you targeted, so invite it. users_not_found means the email on the profile does not match any member of that workspace, which is the usual cost of targeting by email.

What changes in production

A token per workspace, not per app. Each customer installing your Slack app produces its own token. Store it on the profiles belonging to that customer, or on a if you scope by customer already. Tokens can be revoked. An admin removing the app invalidates its token, and sends then fail per recipient rather than globally. Watch for invalid_auth in the logs and prompt a reinstall. Slack rate limits per app. Its limits apply to your app rather than to Courier, so a high-volume broadcast into one workspace is the case to watch.

Get started

Send your first message

Build a notification

Send to many people

Send when something happens

Let users choose

Go live

Move to Courier

Send your first Slack message

Prerequisites

The token belongs to the recipient

Send it

Verify

What changes in production

​Prerequisites

​The token belongs to the recipient

​Send it

​Verify

​What changes in production

Prerequisites

The token belongs to the recipient

Send it

Verify

What changes in production