Is there a way to send an SMS message from another user's account with their credentials?

From what I can understand, Subscriptions would best suit your use case.
Now with my un derstanding, I see 2 options available here

Option 1

1. Use the super admin credentials to log in using the API. Get the access token. Any logic mechanism should work here (3 Legged OAuth,JWT, Password)
2. Once you generate the access token, get a list of all the extensions using the below API
https://developers.ringcentral.com/api-reference/Extensions/listExtensions
3. Loop over all the extensions, extract the ids and create an event filter for all these extensions of the below notification type
https://developers.ringcentral.com/api-reference/Instant-Message-Event
4. Create a webhook subscription with the above eventType (one line item in the array for each extension)
5. The webhook will be called every time there is a new SMS for any of the extensions

NOTE: You need super admin credentials to create notifications for other extensions

Option 2

1. Let each user log into the app individually and get the access token for the user
2. Once you generate the access token, get the extensions using the below API
https://developers.ringcentral.com/api-reference/User-Settings/readExtension
3. Extract the extension id from the response and create an event filter for the below notification type
https://developers.ringcentral.com/api-reference/Instant-Message-Event
4. Create a webhook subscription with the above eventType
5. Use the same webhook URLs for all the users and make sure
6. The webhook will be called every time there is a new SMS for any of the extensions

NOTE: This will require an additional step where every user will first have to log in individually so that the subscriptions can be created for each one of them

NOTE

Sharing a sample code for the Option 1

const serverUrl = process.env.RC_SERVER_URL;
const clientId = process.env.RC_CLIENT_ID;
const clientSecret = process.env.RC_CLIENT_SECRET;
const username = process.env.RC_USERNAME;
const password = process.env.RC_PASSWORD;

const sdk = new SDK({ server: serverUrl, clientId, clientSecret });
const platform = sdk.platform();
await platform.login({ username, password });
const extensionListResponse = await platform.get('/restapi/v1.0/account/~/extension');
const extensionListBody = await extensionListResponse.json();
const extensionIds = extensionListBody.records.filter(({ type }) => type === 'User').map(({ id }) => id);
const eventFilters = extensionIds.map((id) => `/restapi/v1.0/account/~/extension/${id}/message-store/instant?type=SMS`);
await platform.post('/restapi/v1.0/subscription', {
    deliveryMode: {
        transportType: 'WebHook',
        address: 'your host nam
    },
    expiresIn: 7776000,
    eventFilters,
});

@Yatin Gera I understand that I can receive a notification when an SMS is received, but I was to send out an SMS upon an internal event in the system that has nothing to do with SMS exchanges.

For example, if an order is shipped, I want to be able to send an SMS notification from the users direct line notifying them that the order is shipped even if there has never been an SMS communication with the user before. Is this still possible given your proposed solution?