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You can notify all the workflow runs waitingi for a specific event ID. There are two ways to send a notify request.

​
Notify within Workflow

Notifies other workflows waiting for a specific event from within a workflow. 
import { serve } from "@upstash/workflow/nextjs";

export const { POST } = serve<string>(async (context) => {
  const { orderId, processingResult } = context.requestPayload;

  await context.run("process-order", async () => {
    // ...
  })

  const { notifyResponse } = await context.notify(
    "notify-processing-complete",
    `order-${orderId}`,
    {
      orderId,
      status: "completed",
      result: processingResult,
      completedAt: new Date().toISOString()
    }
  );

});

​
External Notification

You can also notify workflows from external systems using the Workflow Client: 
import { Client } from "@upstash/workflow";

const client = new Client({ token: "<WORKFLOW_TOKEN>" });

await client.notify({
  eventId: "order-completed-123",
  eventData: {
    orderId: "123",
    status: "completed",
    deliveryTime: "2 days",
    trackingNumber: "TRK123456"
  }
});

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Lookback Functionality

By default, if you call notify before a workflow reaches its waitForEvent step, the notification will be lost (race condition). To prevent this, you can provide a workflowRunId parameter which enables lookback - the notification will be stored and delivered even if sent before the wait step. This is particularly useful when:
  • You trigger a workflow and immediately want to send it an event
  • You have concurrent operations where timing is unpredictable
  • You want to eliminate race conditions in your event-driven workflows
import { Client } from "@upstash/workflow";

const client = new Client({ token: "<WORKFLOW_TOKEN>" });

// Trigger a workflow and get its run ID
const { workflowRunId } = await client.trigger({
  url: "https://your-app.com/api/process-order",
  body: { orderId: "123" }
});

// Immediately notify it with lookback enabled
// The notification will be delivered even if the workflow
// hasn't reached waitForEvent yet
await client.notify({
  eventId: "payment-verified",
  eventData: { verified: true, amount: 100 },
  workflowRunId: workflowRunId, // Enables lookback
});
When using lookback with workflowRunId, the notification is targeted to a specific workflow run rather than all waiters with that event ID.