Network check
The app stops a send to an address that belongs to a different network.
Same coin name, different network
Some coins can travel on more than one network, and an address can look valid on the wrong one. Coins sent across networks are often lost.
Payments cannot be reversed. If a send has gone to the wrong network, ignore anyone who offers to recover it for a fee.
What the app checks
The address format against the network you chose
When it stops you
Before the send screen, with the reason in one sentence
What it cannot check
Whether the other person’s wallet supports that network
What to do
Ask them which network to use, then make a test send
Check before you send
Fourfold Wallet (sample) is free on iPhone and Android. It holds your keys on your phone and runs the four checks before every send.