Omnibus f4 v4 ,frsky x4r and betaflight

Good morning everyone,I am new to the forums so please excuse any newbie mistakes.
I recently upgraded one of my fc to the omnibus f4 v4 and all is okay on betaflight apart from when I try to setup my x4r receiver I get nothing.
After selecting uart1 on ports and saving I go to configuration and select serial rx and then subs but when I save it the subs choice always changes back to spektrum1024 and I get no response from the receiver.Can anyone help with this problem?