Setting Up Owner Approval When a Site Member Shares the Site

I want to set it up so that when a site member shares the site one of the site owners needs to approve this sharing, I have managed to set it up so it works fine with internal sharing but I want this to work with external sharing also. I have my access request settings set up like all of the guides ask for (see below).

I also have all the correct external sharing settings setup and I am able to successfully share the site as an admin, however when I go to share it on a member's account I get the below error. It's like for the member's it doesn't realise that external sharing is set up properly.

Any help would be greatly appreciated, cheers.