Sandbox credentials are not working!

[geronimo]

For some reason my APIs credentials don't work, I get authentication error. Tried creating them again, but the issue persists.

List of things I tried:
- Calling APIs from both Postman and docs page. For example, using my API login ID and Transaction key here https://developer.authorize.net/api/reference/index.html#transaction-reporting-get-merchant-details
I get: "code": "E00007", "text": "User authentication failed due to invalid authentication values."

- Using Accept.js by copying the exact same both examples from docs(https://developer.authorize.net/api/reference/features/acceptjs.html#Example_of_the_Complete_HTML_Pa...) for sandbox, but changing the API login key and client ID in the code.
I get: E_WC_21: User authentication failed due to invalid authentication values.

The contact support from chat told me to create a thread here to get help on this.
Thanks.

[geronimo]

Issue fixed. I was not using sandbox credentials. The initial switch set in "TEST" mode was confusing me.