You can do this by using an Open Website / HTTP GET action on the primary (sending) device to invoke a Webhook trigger on the secondary (receiving) device.
To simplify setup and troubleshooting, you can create both the primary and secondary macros on the secondary device if you wish, as follows:
First step: create the trigger (secondary) macro. Start with a Webhook trigger. Use something like 'test' as the identifier (using fancy characters for this can cause problems, so stick with a-z and 0-9). Then copy the URL to the clipboard (you will need this URL in the second step). Click OK. Now add a simple test action, for example play a sound or display a popup, then save the macro.
Second step: create the action (primary) macro. You can use an empty trigger. Add an Open Website / HTTP GET action. Paste the URL where it says "Enter URL". Select the "HTTP GET (no web browser)" option. Click OK, then save the macro.
Third step: test the action in the primary macro. When you hear the sound or see the popup from the secondary macro, you know it's working.
If you now transfer the primary macro to the primary device (NB!: the Webhook trigger in the secondary macro will ONLY work on the device it was created on, whereas the primary macro can be copied to any number of devices), and each device is connected to the Internet, everything will work just the same.
