If you are trying to pay via the extension link sent to your device through a notification but it is expired (the link expires as soon as the session expires) you still have options.
You will need to purchase a new parking session to ensure that you have valid parking for the duration that you will be parked.
You will have to go back to the zone in the app to purchase more time.
If you scanned the QR code, you can try to go through the browser on your phone to locate the purchase page again.
If that is not available, you may need to use the app (downloadable through your mobile device or without downloading through the web app here: https://parking.honkmobile.com/signup).
You will have to create an account, and then purchase more time through the zone in question.