What solved the problem for was simple.
I went to create a new sandbox account. Forget that you want to login with the same developer email and allow sandbox to generate and email and password for you. After creating the new sandbox, follow this navigation to copy your test details:
1.Login to your developer account
2.Under Sandbox, click Accounts
3.You will see your newly created Sandbox at the top of the list (I used personal and not business account since I am testing as a buyer)
4.Hover on the three dots icon to the extreme right of the Sandbox, click on View/edit account
5.Copy your Email ID and System Generated Password
6.To be sure it works, go to https://www.sandbox.paypal.com/ and login with the copied Sandbox details
7.Then your done. Go to your app and test.
After testing, you always switch to live mode
