It sounds like the Geo DNS issue, but without more info on what exactly it is you are testing, it’s difficult to be 100% sure.
There are 3 Blynk cloud servers around the world, but a project only lives on one of them - usually the one nearest to you when you created it.
When you use a device to connect to blynk-cloud.com then some clever DNS stuff happens to ensure that the device hots the correct server. The same when you log-in with your app.
However, this doesn’t work with API calls.
If you make an API call in your browser using the blynk-cloud.com url then it will work if your nearest server is the one that contains the project. If not then you’ll get an invalid Auth code message returned, because the server that your API call hit wasn’t the one that contained your project - so it said “I don’t have a project that contains that auth code - sorry”.
If the guy who is in Europe is getting a success then the project probably sits on the Frankfurt server. It’s IP address is
22.214.171.124 and this is what everyone else, as well as any IFTTT recipes should be using for API calls.
If only the guy in Canada was having success then this would mean that the project sits on the New York server, whose IP address is