Consideration was always in interesting discussion by our company's general counsel when going through training.

On thing that stuck out to me was the company would always review entry criteria if it may any requirement beyond what would be commonly available to the lowest ranking member of society. This was typically considered to be a computer with internet access as it was likely to be available at a public library.

While mail has become a more accepted means of non-consideration entry, I believe there was a time where it was considered consideration. Counsel argued that mail-in entries required the submitter to own or purchase a stamp, a postcard, a writing device, and potentially an envelope for the postcard.

An "app only" contest was given extra scrutiny because it required the user to own some sort of smartphone or mobile digital device.

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While, that was contests and promotions (in which case, they needed to avoid running an illegal lottery), I imagine a similar argument could be made for WhatsApp. WhatsApp is only available if you own a smartphone capable of downloading the app.

Of course, German contract law is very strange and alien to every other legal tradition (except Japan, I think, and that‘s only because they modeled their civil law on ours).