If you goto send Bitcoin Cash from the Coinomi Bitcoin Cash wallet and Scan an address it will try switch over to calculating the BTC price, and try to send bitcoin, then give you an error message before you can send.
(you wrote down your seed and set up a password right?)
The fix, till they update the app:
Scan the address, Copy it, then Paste it.
it will ask if if you want to send Bitcoin or Bitcoin Cash
hit Bitcoin Cash and continue.
This issue only happened on my first attempt to send. After that it seems to be working properly.
I posted on the Local bitcoins forum and someone else had the same issue. Others have not. I'm on a Pixel XL with stock Android 7.1.2