Fulfill Sync is able to sync the tracking info of orders that are fulfilled (with Fulfill Sync) to PayPal.
1. Navigate to https://developer.paypal.com/ and login with your Paypal account.
2. In My Apps & Credentials, choose Live and click on Create App.
3. In Create a New App, enter the App Name as Fulfill Sync, select the App Type as Merchant and click on Create App.
4. Copy the Client ID and Secret.
5. Open Fulfill Sync app and click on the Sync Tracking info to PayPal.
6. Paste the Client ID and Secret in the respective fields and click Save.
Every time the source fulfill orders, Fulfill Sync will also check if the order is present in PayPal. If the order is present, the tracking info will be updated as well.