Toll-free numbers are allowed as long as your country code is included. The reason is that toll-free numbers without country codes cannot be uniquely identified — the same number can apply to two different countries.

Also, a requirement is that the phone number onboarded is able to get a phone call or SMS for the registration code. 

At the same time, many 1800 or toll-free numbers are backed by an IVR (Interactive Voice Response), while WhatsApp registration calls are not able to navigate an IVR. To enable that registration, tyntec will provide you with two sender IDs upon request. You can use this information to create a whitelist for those numbers — so that once the call comes in, you can redirect it to an employee or mailbox where the registration code will be captured.