There's no point in asking about PayPal integration.

Hey there
My shop is powered by OpenCart 3.
The link to the PayPal Commerce Platform appears to work OK, but when I try to save the settings, I receive the following error message:
Authentication failed because the authentication credentials were invalid or the authorization header was missing.
There are no clear instructions in the FAQ about this error message, so I turned to my PayPal account for help - unfortunately, the advice is as unclear as mud, and it seems to refer to an earlier version.
Thank you in advance for any assistance.