CORS preflight request returning “403 Forbidden”; subsequent request then only sending in Chrome?

As mentioned in my comments, this appears to be an issue with your server. For some reason, it is rejecting the initial OPTIONS request. You will need to look at your server logs to see why your server is responding to this request with a 403.

It's taken me a week, but I've finally found the problem.

I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.