The error message you’re seeing indicates that there’s an issue with the authorization. This usually happens when the application ID or location ID you’re using is incorrect or not properly configured.
Please ensure that you’re using the correct Sandbox application ID and location ID. These can be found in your Square Developer Dashboard under the Sandbox section.
Also, make sure that you’re using the correct Sandbox URL (https://connect.squareupsandbox.com) in your code.
If you’ve checked these and the issue persists, it might be worth double-checking your entire setup process to ensure all steps have been correctly followed.
This answer was reviewed by @Bryan-Square.