Changing upload folder to subdomain

So I would like to move my media library to a subdomain on my server. I was able to successfully create the subdomain, transfer all my old files and run a SQL script to change the URL in all my posts.

I am having an issue with uploading new images via the Media Library.

Whenever I try and do so, I see a broken link and even though the URL seems to be right, the image file never makes it to the subdomain folder. I can manually upload the file to that location via FTP and the image link in the Media Library starts to work again.

How can I prevent this and only upload new images via the Media Library to a folder within my subdomain?

Any help is appreciated.