IBJoel, what are you seeing?
I checked the feed with the w3c feed validation service and it's returning data. (though it complains about some of the content which are minor complaints about the format and content of the feed, it does return feed data and not an http error, please check it yourself.)
https://validator.w3.org/feed/
Error 403 implies that FT may be blocking ifttt. Can you check for that to see if ifttt been blacklisted somewhere? Surely there's a log somewhere?
I'm sure there's a lot of FTers using ifttt to check for new posts in this forum. It was publicized when they decided to move to separate threads for each deal in that forum. No idea if it's working in any other forum but it's very easy to set up a free account in ifttt and create your own applet to try it or to use the w3c feed validator to check it as well.
Error 403 info:
https://developer.mozilla.org › Web › HTTP › Status
Jul 8, 2021 — The
HTTP 403 Forbidden client
error status response code indicates that the server understood the request but refuses to authorize it.