Angular not communicating with ASP.Net after publishing to IIS

Question

I have a problem between Angular and .Net-Core after I publish to IIS.

The app runs fine on my local machine but when I publish to IIS the Angular app can't talk to the .Net app.

I can see the home page, but can't do a search on the page (which communicates with the API and DB)

Where do I start to debug this? What can I do to debug where the error is coming from?

Should I start looking at the configuration between the two apps or something on the server (IIS)?

I have an error.interceptor.ts file that does this:

export class ErrorInterceptor implements HttpInterceptor {
  intercept(request: HttpRequest < any > , next: HttpHandler): Observable < HttpEvent < any >> {
    return next.handle(request)
      .pipe(
        catchError((error: HttpErrorResponse) => {
          let errorMessage = '';
          if (error.error instanceof ErrorEvent) {
            // client-side error
            errorMessage = `Error: ${error.error.message}`;
          } else {
            // server-side error
            errorMessage = `Error Code: ${error.status}\nMessage: ${error.message}\nStatusText: ${error.statusText}`;
          }
          window.alert(errorMessage);
          return throwError(errorMessage);
        })
      );
  }
}

and in the window alert I see this