In order to use SMS, you will need to purchase credits.
You can send an SMS to a tenant a couple of ways:
using the actions button from the tenancies list next to each record, click on "send SMS"
view the tenancy record and at the top use the actions button to "send SMS"
view the tenancy record and scroll to the bottom. Click on the "communications tab" and click on the send SMS button on the right hand side.
Sending an SMS produces a pop up where the subject and body can be edited.
The name of the tenant will be shown along with the letting unit address.
Type the text you want in the message box and the counter will indicate the number of characters and credits being used.
In order to save credits, where there are multiple tenants on a single tenancy, the SMS will only go to the first named tenant and not to others.