Add-On Domain – Search Engine Indexing – What am I doing wrong?

So I have recently installed WordPress (www.seanbeeson.com/thecomposerscorner or https://www.the-composers-corner.com) on my server with an existing Joomla website (www.seanbeeson.com) and have setup https://www.the-composers-corner.com as an add-on domain pointing to the wordpress directory.

I am however noticing that google is not really indexing my site nor is my site really ‘holding’ the add-on domain. I know I am missing something really simple (or at least I think I am? :P) and after having scoured a number of posts about changing config files and pointers I figured I would just ask at the expense of feeling like an idiot haha

Any ideas what could be causing this and how I can fix it? Thank you in advance.

Sean