The link you provided is not Find, but an implementation that calls to find. Without knowing about the implementation it's impossible to know why it is returning 403. You would need to contact developer support for further assistance 

Having taken a look at an OOTB install of Find I can see this issue too. From what I've seen, the issue is in the way that the AutocompleteController (shipped as part of Find in EPiServer.Find.Framework.UI.Rest) is handling JSONP requests (i.e. requests with a "callback" parameter). Ultimately this looks like a bug.

I'd assume the request isn't cross-domain and so there's not a reason why it couldn't be made as a standard JSON request rather than a JSONP request so, as a workaround, you could change:

dataType: 'jsonp'

to

dataType: "json"

in your jQuery ajax call. This should remove the "callback" parameter from the call and cause the controller to return just the JSON data rather than wrapping it in a callback. As you're using jQuery, the implementation and processing of the call behind the scenes is masked and so the remainder of your JS shouldn't need altering and the autocomplete should start working again.

Hey Paul, thanks for the reply.

But can you please tell from where data is coming?

It is an ajax call and this path isn't in my code

https://integration.english-heritage.org.uk/find_v2/_autocomplete

As far as I'm aware, the stats are held within Find and that API is a way of accessing them. The API endpoint '/find_v2/_autocomplete' maps to EPiServer.Find.Framework.UI.Rest.AutocompleteController within the EPiServer.Find.Framework library which is a core part of the Find client and hence will have been added when you added Find to your project.

I am also running into same issue when trying to test it on AlloyDemoKit. Did we got solution to above problem? Thanks in advance for the help.

Below is URL which gives 403

http://localhost:2030/find_v2/_autocomplete?prefix=Alloy&size=5&callback=jQuery19105857890212712183_1592757241792&_=1592757241795