switchMap is not executing its code in Http Interceptor

Please note, am facing an issue with the switchMap in interceptor. Only in the interceptor am facing this issue, but in angular service it works fine. unable to find the reason why switchMap is not executing its code in interceptor. Need help please.

intercept(req: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {

return this.authService.getAccessToken().pipe(
switchMap(token => {
const headers = new HttpHeaders({
'Authorization': `Bearer ${token}`,
'Accept': 'application/json'
});
const clonedRequest = req.clone({ headers });
return next.handle(clonedRequest);
})
);
}

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