In order to start sending SMS messages from your Yay.com mobile app, there are a few steps that need to be taken.

First, you want to go to 'More' in the bottom right-hand corner of the app from here, you want to select 'Settings' and open the chat settings then, click 'Messaging Caller ID' and select an SMS ID. Do note that you will need to have a UK mobile number on your account and alternative caller IDs added to the account will not work for this!

Once you have selected the SMS ID you are going to send messages from your just need to find the contact that you wish to message, then, once the contact has been selected you just need to click the 'SMS' button and it will begin an SMS chat with the contact.