Did you enable GPIO pins in raspi-config?

Have a look at Locative-app for IOS.
It works with json. In the past I used it to turn on/off a switch when I was several meters (300+) from my home. For what I know you van make the range as big as you want.
Haven’t tried it since I closed all the ports on my router and started using a VPN.

The same strange thing happened to me on my 5 day old fresh install on a Raspberry Pi 2B with Raspbian Stretch. It worked without any problems. Today I noticed the same failure in the logging.
Your solution worked for me. Thanks for posting.