Hello @CallaghanWildrew
As per JRASERVER-5493, you can’t add a watcher during Issue creation with Jira SERVER.
As per the How to ask a good question thread, please provide the full example of how you tried to add a watcher to an Issue after the Issue was created. Include the full request in the code language you are using and any errors / responses you are getting. Also, which version of Jira Server are you using?