To kind of combine the others comments and add some more depth:
HTTPS runs over port 443, and port 80 is normally for HTTP only.
Most people setup their webservers to serve HTTPS over 443 and redirect port 80 to 443 so anyone that sends something to `http://example.com` automatically gets forwarded to `https://example.com` (and then the browser can tell them to ONLY use the HTTPS version from that point forward)
This is a generally "acceptable" tradeoff between usability and security.
But when you control the API and the client, you can know that you will never send credentials over HTTP, only HTTPS. So you should have nothing coming over port 80.
Then, with a simple script, you could set it up so that it will accept everything on port 80, and if it includes a token of some kind from your app, it logs the request, then marks the token in your database as "expired" so it can no longer be used anywhere (even on port 443).
There's a kind of attack sometimes called "SSLStrip" which can block all requests for someone to an HTTPS version of the site, and in many cases can trick the client into trying the HTTP version if the HTTPS fails. This kind of thing would not only stop that attack, but it would also log it and ensure that any tokens sent that way would be instantly expired, so that the attacker (who saw the tokens when the client tried to send them) can't use them.
There are other reasons too. It will notify you of any developer-mistakes that are sending credentials over HTTP (it's a one letter difference, and despite the best efforts sometimes these kinds of things slip into a codebase as typos or a dev just not thinking), and it can help you tell "scanning" traffic from "normal" traffic (since nothing in your app will ever talk to port 80, so everything on port 80 is "bad" and can give you some clues into what attackers are trying on your network).
And the best part is that it's easy! I could probably throw something together for our API servers that does this in a day or so start-to-finish. That's a REALLY good ratio between time spent and security benefit that you normally don't get!
Requests sent to port 80 will (usually) be unencrypted HTTP traffic, hence revealing the secret token to anybody listening in between the client and the server. Someone may accidentally send an HTTP request either by typo or lack of knowledge.
