So today while working within WebApp Builder I had an app which requires the near me feature and needed this to embed on my own website.
I tried using the
allow = "geolocation"
And it still gave me that error.
I did some more digging on the Browser Devs forums and discovered a way which I think for anyone who faced the same challenges like I did today could also get things working.
I found out that you have to use it this way;
allow="geolocation *;"
As as described in this post, grants access to all origins loaded within the iframe.