Payment error: Client Authentication failed

Hello, the blanks descriptions on your form for payments are confusing and without descriptions of what info is required. I need someone to walk me through it. The image is the error message I get when filling out the form.

Generally, this issue occurs when the credentials used are incorrect or incorrect payment mode is selected (live or sandbox). We request you to check the credentials used on the form and change them accordingly in the payment wizard. Also, please make sure that there are no leading or trailing spaces in the credentials used.

If you need any further assistance, please let us know. We will be happy to assist.  

Thanks.