Well I thought I asked another question but apparently it didn't post.
I was having some issues getting it to work on iOS because of cross domains/cors issues but I've managed to figure it out.
If anyone else is having problems getting this to work on device then you just need to add this to your 'request url' & 'web_app_url'
https://cors-anywhere.herokuapp.com/
- add it to the front and then just have your normal google sheets/script request after the /
Like: https://cors-anywhere.herokuapp.com/https://script.google.com/macros/etcccc
It acts as a redirect to bypass the CORS requests.
Hope that helps someone!