Hi all, 

I have experienced the same issue but managed to resolve it on my end. It appears that the Odoo documentation is unclear. 

Please try these steps to configure correctly. Please note I am using sandbox environment. 

1. Log into the Paypal developer dashboard, you will have 2 sandbox accounts set up automatically. 
   The Merchant (business) and personal (as a Consumer). 
2. Create an API app for the merchant paypal email address.
3. The client ID and secret key will be generated. 
4. Log into paypal using the merchant account credentials (See Sandbox accounts for credentials).
5. Navigate to Account settings > Website payments to set up the payment data transfer that will generate the Identity Token which we will use as our Webhook ID.
   

Getting your Client ID and secret key, and the merchant account credentials for Step 4.

To get your Webhook ID

Hope it helps.

Regards,

Audrey Ng

3D Photomation Pty Ltd

same here