GetUser API Request Returns Authentication Error: 105, InvalidCredentials, `Authentication failed. Either supplied credentials are invalid or the account is inactive

Question

I have using sandbox environment , as my account url starts with ui.sandbox.bingads.microsoft.com/ but when i am trying to fetch the ids of customer and account programmatically using customer management service with getUser or getCustomerInfo then i am getting error with 105 code. (Either supplied credentials are invalid or the account is inactive). I had check credentials and status. Now help me with the same to resolve error. I have created account using gmail then also created account using outlook-int and given alternative email id as same gmail. now when i login to devleoper it is giving me that my id is suspended. I had appeal for the same but still i expect that i have account with other gmail account should work.