Hosting a subdomain without the main domain

Hi All, (TL;DR) To summarise, I'd like the following [COLOR=rgb(184, 49, 47)]primary.com --> cloud host provider (ip: 11.22.33.44) - works! [COLOR=rgb(65, 168, 95)]examplea.com --> cloud host provider (ip: 11.22.33.44) - works! [COLOR=rgb(65, 168, 95)]dev.examplea.com --> cloud host provider (ip: 11.22.33.44) - works! [COLOR=rgb(41, 105, 176)]exampleb.com --> AWS EC2 instance (ip: 99.88.77.66) - works! [COLOR=rgb(251, 160, 38)]dev.exampleb.com --> cloud host provider (ip: 11.22.33.44) - doesn't work! The long explanation... I have a some hosting using cpanel along with a free domain that came with it [COLOR=rgb(184, 49, 47)]primary.com hosted from /public_html I also have an addon domain hosted at another registrar ([COLOR=rgb(65, 168, 95)]examplea.com) using their nameservers. I updated the A Records for @ and * to point to the shared ip of my hosting (ip: ). I also updated /etc/ips.remotedns to include both ips of the domains nameservers. I have configured[COLOR=rgb(65, 168, 95)] examplea.com hosted from [COLOR=rgb(65, 168, 95)]/examplea.com. I can access both [COLOR=rgb(184, 49, 47)]primary.com and [COLOR=rgb(65, 168, 95)]examplea.com and their respective website is displayed. I can create the subdomain [COLOR=rgb(65, 168, 95)]dev.examplea.com and that is hosted from [COLOR=rgb(65, 168, 95)]/dev.examplea.com and is also accessible via the web. Here's where my problem starts. I also own one further domain [COLOR=rgb(41, 105, 176)]exampleb.com which uses the same nameservers as [COLOR=rgb(65, 168, 95)]examplea.com. [COLOR=rgb(41, 105, 176)]exampleb.com's A records currently point to an aws server (ip: ) which is serving as the web host for that domain and I'd like to keep it that way. I would like to create a subdomain called [COLOR=rgb(251, 160, 38)]dev.exampleb.com and host this at the hosting for primary.com but leave [COLOR=rgb(41, 105, 176)]exampleb.com pointing to AWS So i have created the A record dev and pointed it to the share ip of my hosting. If I use add subdomain, my tld [COLOR=rgb(41, 105, 176)]exampleb.com is not an addon domain so that won't work So I am trying to add [COLOR=rgb(250, 197, 28)]dev.exampleb.com as an addon domain instead, but I cannot seem to get this to work. Cheers, Matt