You must enter your mobile number into WhatsApp X after you open it. Simply type it in the bottom field. When you click Verify, you will be asked to enter your phone number. You will need to enter the word YES in lowercase in the chat window and then tap Verify if this is not an Android phone. A verification code will be sent to your Android phone. Click Verify to verify it.  If both the WhatsApp X beta app and the original WhatsApp are installed on your device, the WhatsApp X beta app will prompt you to scan a QR code on your phone. WhatsApp X should now work just like it did before it was scanned