Currently, there is a quota of 4 sites with the Search Atlas SEO Add-On.

After confirming with support, there is no current method for me to have more than 4 sites added for a sub-account client.

I would like to be able to sell/resell additional site quota through the SEO Add-On so that I can offer a seamless way for my clients to purchase quota for their sites if they have more than 4 sites.

Reference - Heading SEO Feature Quotas on this page: https://help.gohighlevel.com/support/solutions/articles/155000004723-get-started-with-ghl-seo-a-guide-to-boosting-your-search-rankings