Test environment credential is not working for Transparent SDK

Hi, I am trying to use the Transparent Checkout SDK, and I want to test for it.

I saw the test environment is supported for Transparent Checkout SDK, but when I try to use the test environment credential to init the SDK, I keep receiving 500 error.

Is the test environment supported by Transparent Checkout SDK? If yes, how can I fix it?

Thank you for your help