Option to send SMS Text to recipients. The SMS Texting must be setup first, see this Configuring SMS Text Sync.
Send SMS Text in designer custom action
Action Name -- sets the name of this action
Execution Status -- whether to show to the user or not when running this Action
Recipient
From -- this will be one of the phone numbers assigned to your account by Twilio
To -- choose Recipients from this dialog box. The Recipient option chosen must be a phone number that can receive texts.
For Users and Groups, the system will seek to determine the cell phone number associated with the user (for the Group, it will determine the members and look up each one's phone number).
For Column, it needs to be one with a phone number in it.
For Phone number/placeholder, the number is entered directly (placeholders that pull info from the form can be used).
Fetch user phone number from -- option of User Profile or Active Directory
SMS Body
Body -- a message up to 600 characters. Placeholders and expression can be used to take in values from the SharePoint item. When using placeholders, you have to determine if the value that will be added might cause the message to exceed 600 characters. Click "Add placeholder or expression to body" to bring up the dialog box where these can be added.
Disable SMS Editing -- the text that will be sent can be shown to the user (the one who clicked the button to launch the Custom Action) so that it can be edited in real-time prior to sending. Checking "Disable SMS Editing" prevents the edit box from showing to the user. See below for an example of what the "edit text" box looks like.
Log messages - logs the message in a list in the Site, usually "SMS Text Log - Outgoing"
NOTE: This error will show up at the top of the Action if SMS Texting is not configured for this Site:
Refer this video for more detail: Send SMS Text