How to fix Session is not started. Call POST /sessions/:id/start first.

[sakibstime]

Hello,
I tried to connect to the second session through the QR Code. But the QR code cannot be generated. So, I tried to connect using "Link with Phone Number". But after clicking on the "Generate Pairing Code" button, getting the following error,
Session is not started. Call POST /sessions/:id/start first.

Screenshot: https://imgur.com/a/mcG8zT8

How to solve this?

TIA

[tt-a1i]

The second session has been created, but its WhatsApp engine has not been started yet. Those are separate steps in OpenWA. The pairing-code endpoint checks for a live engine first, which is why it returns that exact message (check in requestPairingCode).

In the dashboard, close the pairing window and click Start on the second session's card. The Start action calls the session start endpoint and then opens the QR/pairing window (dashboard flow, Start button). Wait until the session reaches the QR stage before generating the phone code; the whatsapp-web.js adapter deliberately rejects pairing requests made before QR_READY (readiness check).

The equivalent API sequence is:

POST /api/sessions/<session-uuid>/start

After the session status becomes qr_ready:

POST /api/sessions/<session-uuid>/pairing-code
Content-Type: application/json

{"phoneNumber":"<country-code-and-number>"}

The phone number must be 6–15 digits in international format, with no +, spaces, or dashes (request format). If Start never progresses to qr_ready, that is the point to check the second session's server/Chromium logs; retrying Generate Pairing Code while it is still stopped cannot initialize it.