WhatsApp doesn’t let you send messages to people not in your address book.
Most of the time this works because why would I want to message strangers anyway.
Sometimes though this is useful. For example, a number of times there are delivery people who ask for the address and there’s really no need to save their numbers to be able to send the address and location.
The OnceMessage app solves this problem by letting you do just that. Just enter the person’s number prefixed with the country code and it will open WhatsApp so that you can message them directly.
None of the information entered is collected or stored.
Also, there are no cookies used in this app.