API Authorization method not working described in docs

I am trying to authenticate api requests using authorization header Basic ${USERNAME}:${PASSWORD} but I am getting following message:

{ message: "'bXVoYW1tYWRzYWxtYW4yNDcxMDA2QGdtYWlsLmNvbQ:OIZC6WzofcOLpcywZDtmO' not a valid key=value pair (missing equal-sign) in Authorization header: 'Basic bXVoYW1tYWRzYWxtYW4yNDcxMDA2QGdtYWlsLmNvbQ:OIZC6WzofcOLpcywZDtmO'." }