You will need to have a Brightspace instance setup and running to use SMS. Please work with Brightspace Support to get one set up if you don't already have a functioning instance. Once you have a Brightspace instance running, follow the instructions below to setup SMS integration.
Login to your Brightspace instance as a Super Administrator

Go to Admin Tools -> Users

Click New User

Set the following fields:
SMS.UserSMSUser
Set ‘Role’ to Super Administrator, then check the ‘Manually set password’ checkbox and set a password for the SMS User account

Click Save. This new SMS User account will be used when authenticating SMS later in this guide

Go to Organization Related -> Manage Extensibility

Click OAuth 2.0

Click Register an app

Fill out the required fields with the following values:
SMShttps://sms.invalid/callbackenrollment:orgunit:create,delete,read grades:gradeobjects:read grades:gradevalues:read organizations:organization:read users:userdata:create,read,update users:activation:read,update core:*:*72000
Uncheck Prompt for user consentand check I accept the Non-Commercial Developer Agreement (after reading the agreement)

Click Register

You have now registered SMS in Brightspace and a Client ID and Client Secret have been generated for use in SMS. We will use them later on in this installation guide. If you close the window before we need them again, you can always retrieve them by returning to the OAuth 2.0 Apps List (by following steps 1-3) and clicking the name of the application you just created.
In order for the contacts sync feature to function correctly, some permissions and features must be enabled first:
<aside> ⚠️
If you cannot access the “Relationships” tab when viewing a User in the Brightspace applications and/or the SMS parental sync feature is not working, try disabling and enabling the Brightspace Parent & Guardian tool under Organization Tools. If that doesn’t work, ensure your current user’s role has the correct permissions to view relationships (described below)
</aside>
Go to Organization Tools and ensure that Brightspace Parent & Guardian is enabled:

Under Options → Security → Roles and Permissions, update role permissions for the Super Administrator role:

