I have a running server (windows) with Node-red which send me various notification to connected devices via WhatsApp and emails thru Internet. I need to receive those notification in case of internet is down, while connected devices (Andorid, Iphone and so) are in the same network as the server (same LAN). Controlling node-red is working in this scenario because I'm connecting directly to Node-red Lan IP address, but notifications from Node-red are not working.
I need to receive those notification even when I'm sleeping and the phone screen is off (internet down).
On android you can use tasker or automate, there is a network plugin that can receive http request , or there are mqtt plugins. Nevers used an Iphone so can not help there.
Many people use a silent mode overnight to prevent notifications till the morning so watch out for that. Also, if the phone isn't plugged into power (and possibly even if it is), the power-saving modes of the phone may limit notifications depending on settings.
A different approach would be to use either a microprocessor device or a Raspberry Pi with a light/buzzer.