Can't get domain mapping to work

Hi there,
I can't seem to get the WordPress domain mapping working. I've set the A records for nosh-online.co.uk to the correct IP address and updated the subsite by editing the site url in the subsite but I get the following error message;
"This site can’t be reached
nosh-online.co.uk’s server IP address could not be found."
Can you help please?

Regards,

Steve