Your API key for the channel. After you created a new applet with the maker channel go to ifttt.com/maker and click on Settings in the top right corner. You will now see some infos – here the URL part is important. Copy the last part of the URL into the Key-field in the IFTTTTrigger-op settings. E.g. 12345-12345678 for the URL https://maker.ifttt.com/use/12345-12345678.

When you create a new applet on IFTTT you will be asked for an event name for the trigger, use something like button_pressed (without spaces). This has to match the one you enter in the applet setup.

When pressed or triggered by another op it will trigger the recipe on IFTTT.