Welcome to the Make community!
Upwork does NOT have a webhook option. You cannot use a Custom Webhook’s URL with Upwork.
Follow the advice from the others provided above to connect using the HTTP Make an OAuth 2.0 request module, or use the Upwork community integration found here: https://www.make.com/en/integrations/upwork-community
Hope this helps! Let me know if there are any further questions or issues.
— @samliew
P.S.: Did you know, the concepts of about 70% of questions asked on this forum are already covered in the Make Academy. Investing some effort into it will save you lots of time and frustration using Make later!