How to add an icon to a browser tab

Browser: Safari, FireFox, Chrome
Platform: mac OS
Page type: .php

I placed the following code into the Header:

<link rel="icon" type="image/png" href="https://www.PriorAuthorization.us/assets/images/icon.png" sizes="16x16"/>

It will not display. Does it require another line of code? The path works. I don’t understand. Any suggestions would be appreciated.

Thank you in advance.