Unable to make REST API GET request in A360 - Proxy authentication required. Username or password is incorrect.

I get the error message “Proxy authentication required. Username or password is incorrect” when trying to make a REST API GET request in A360.

I’ve verified my credentials are correct as I’ve tested the request in both Postman and v11 (with the same exact URI/headers/credentials) and can can make a successful GET request, but when I try making the same exact call in A360, I get the above error.

URI = https://mydomain.com:port/rest/v1/administration

Headers = {authorization : authID, accept : application/json}