"Answer", I think! My IFTTT applets (recipes) now work, anyway. I can now use IFTTT to enable other actions arising when an Arduino simply sends web requests.
Sorry.. this could be more clear? But if your IFTTT/ Arduino project DID work, but then stopped, have a dig? Others don't need to!
Background: I did my first IFTTT work in Feb 2017. There were a few false starts, of course. Not least in "who" I would "be" in my relationship with IFTTT.
(By the way: I would not, if I were you, connect via a Google account I use for anything else. Or use the "Continue with Google" means of logging in. Do the latter, and it seems you give IFTTT full access (read/send as/delete) access to gmail accounts connected to the Google account you "Continue with" (log in as). (Oh... and stuf you do connected THAT way won't be "visible" when you are logged in with an IFTTT user ID/ password.)(I have a for-this-only Gmail account which I use for IFTTT, and an email address elsewhere that I only use as the destination for emails from IFTTT applets. Happily, the "elsewhere" allows me to forward emails arriving there on to one of my "used every day" eddresses. But once the email has left the IFTTT applet, IFTTT knows nothing of where it goes from the first destination. I don't like my peas touching my carrots.)
ANYWAY... looking at the logs of my applets' activity (Get Started - IFTTT where xxx is applet ID, given at bottom of page, when you go into "Configure" (settings) for a particular applet (or drill down to an applet's settings page, and click "view activity log") I thought I could see things WORKING... in the early days (Feb 2017), and then stopping working... though when I try to double check that now, I can't see it again. (Can find LOGS, just can't see what I recall.) Also, I'm pretty sure that I created Maker/Webhooks (same thing, different eras... name was changed) apps successfully in my early days, and then, 7/14, found they WEREN'T working.
"Webhook app that was working": All I wanted to do (and now can do again!.. details coming) was to set something up at IFTTT which would, when a web request went to my "secret place" at IFTTT (it can be sent from Firefox for testing, but ultimately will be sent by an Arduino in response to an event. It can even be sent WITH DATA, i.e. "a payload" (say, the temperature, at the moment, where the Arduino is).... and have that web request give rise to an email. The email will contain the data, if you set it up that way. (Or you can do other things in response to the web request... but I am starting with getting an email sent. Other things: Post to Facebook, SMS, etc.
SO? What was "the problem"? Somehow, my Webhooks key was set up wrong. At Get Started - IFTTT I was seeing "Account Info... Connected as AUserID", where "AUserID" was something created by me... a while ago. It was NOT the user ID I am currently using with IFTTT.
Clicking the "Edit Connection" button on that page is a bit drastic. You'll get a new... "webhooks key"? I.e. your code for creating triggers. The string of gibberish (which you should keep secret.. it is sort of a password) reported to you at the end of... "URL Webhooks works better with IFTTT((gibberish here)) on the page we have been talking about here.
Because you get a new key, old apps will stop working. I think. But maybe they weren't working already? All you need to do to fix them, if this is all that is wrong with them, is update them by replacing the old webhooks key (or whatever is the right term!) with the new one.
Ordinarily, I would now mark this thread "SOLVED"... but given my uncertainty about whether I've REALLY solved it, and also in hopes that others will post, saying they had similar experiences between Feb 17 and 15 Jul 17, I won't. Or maybe people who know more about IFTTT have "answers" as to how my Webhooks "connected as" could have got out of step with the user name I was logging in with.