Let’s face it, debugging gtm in devices other than desktop is hard. Debugging in IOS is harder because gtm debugger toolbar doesn’t work on it.
The tip to help debugging IOS is to be able to debug it from desktop
Let us use the ios webkit proxy debugger
Follow the installation instructions. However this debugger doesn’t let you inject js when debugging.
We will need another tool like https://github.com/artygus/webkit-webinspector – just follow the installation instructions. then go to
http://localhost:8080/Main.html?ws=localhost:9222/devtools/page/1 and you can start debugging as if you have the dev tools.