Well then seems you use WkWebView, therefore welcome to the club “I’ve got problem with CORS and WKWebView” (and that is the reason why it works on Android and not on iPhone)
Not your plugin, but the WkWebView Ionic plugin have got a relevant issue about that:
You could try to remove WKWebView and it most probably gonna work.
Otherwise, in the issue listed above, some guys found work around to solve the problem.
If you find something I would love to hear about it, I never till today found a way 