Share problem with Whatsapp

Good day dear developer team,

we have a problem with the Whatsapp share button. Only on cell phones or small displays, the Whatsapp button appears on our pages. If you press the share button, you are not taken to the Whatsapp app as usual and can share the page, but you are redirected to the Whatsapp website and asked to install the app, even though it is installed on your cell phone. Do you have an explanation for this?

Many thanks in advance for your help and already once a nice and healthy weekend.

Andre

The page I need help with: [log in to see the link]