Send SMS from local handset

I’m building a management app that only staff can use to generate a one-time access code that people can use to access one of our platforms. Workflow is something like this:
1 staff opens app
2 inputs user’s mobile number
3 presses “send code”
4 app generates a random code locally on the handset
5 pushes the code in an SMS from the staff member’s handset to the user’s mobile number
6 pushes the code via an API to our servers so it’s ready to be used
7 dumps the code on the handset, ready for the next number

I’m struggling with step 5. I’ve seen a couple of comments about working with SMS but none of them really have answers. Is there a limitation from the manufacturers to explicitly stop this from happening or is it an AppGyver limitation?

This may be possible by going through a third-party service like:

Your workflow is a bit messy. You cant generate random/one time features like this in the client side application(in your case, the app). Security maybe is not an issue at this time for you, but if you do this way, the user can sniff the code without receiving the sms.

Also, you cant send sms in the name of of the staff. No app has the power to do that(its not an appgyver limitation). The sender number of the sms, will be determined by your backend or 3rd party server.

The workflow need to be something like this :

1 staff opens app
2 inputs user’s mobile number
3 presses “send code”
4 the button pushes the code and mobile number via an API to the server
5 Your server(or 3rd party service) send the sms to the mobile number requested.
6 APP receives the input, and checks in the backend via api if the data is valid.