I'm receiving an error on transaction message

I am testing out a sales form. I enter all the information and submit it, but I receive an error on transaction message. "User authentication failed due to invalid authentication values. Go back and fix. " What does this mean and what do I need to fix?

Thank you

Hello,

Please make sure that the ID and Key are correct and working. Please update it when needed and try it again. If the issue still persists, please let us know so we can investigate it further.

Thank you!