Unfortunately, the remote access is not allowed with HomeKit Unless you have an Apple TV (since the 4th Generation) and / or a HomePod connected to your Home network, to be the one that sends the instruction to open or close the door to the ismartgate.

You can even associate an iPad to act as a bridge, here are the instructions to make the Apple devices compatible a Bridge.

Please note that to create Automations you would have the same requirement as for the remote access. Here is more information about automations.