On PackageRadar website «Customs clearance in progress» status means these statuses of Swiss Post:
Tracking package of Swiss Post
With the use of our tracking form you can easily check the status of your package. Also if you want to tracking Swiss Post and get your package location updates to your e-mail, you can Register on our website.
Swiss Post — is not the only postal service that you can track at PackageRadar. See full list of postal services available.