During the verification process the telephone number to call when you install WhatsApp, you can go to be notified by SMS verification failed error. This prevents the configuration process WhatsApp is conducted properly.
Most of the time the error occurs when you try to install WhatsApp Plus (which is a modified version of the original application), but can also happen with the original version.
If this happens, try these solutions, in this order, until the error occurs.
Install the latest version of WhatsApp: sometimes older versions can cause this type of problem.
Check carefully that the phone number you entered is correct. You must select your country and then enter your number, no prefixes and no symbols or spaces.
Check that an internet connection is active (4G, 3G or WiFi). If at the time you request verification through SMS you have not activated any data network, or for some reason those to which they are connected are not working, you'll get the error message.
Last attempt: reboot the phone, and then repeat the verification procedure.
If you still did not work, use the Voice Verification option: the code is a very clear statement by automated voice over the phone. A good choice.