Unable to obtain an oAuth token in development. Error states "Invalid resource owner credentials"

So, I have been trying to get the Call Log API set up and am going through the development process. I created an app and ensured that I can login to both login.ringcentral.com and developers.ringcentral.com using the same credentials for both areas. The "Try It" button shows that the app has permissions so I have tried obtaining an oAuth token by sending an API request to https://platform.devtest.ringcentral.com and get an "invalid grant" error with a message of "Invalid resource owner credentials" I have tried sending the request via postman and via the ringcentral gitHub API explorer (https://ringcentral.github.io/api-explorer/#!/Authentication/oauth_token_post) and both return the same error. I am using password as the grant_type and have confirmed that the app I created does support the password flow. The app credentials even show "Active" for the password in the sandbox area. I am using 14243227530 as the user. I have also tried using the email associated with the account but have had no luck. Please let me know what I am doing wrong. Thanks!