Great question — answering as the UphillTech team:
It sounds to me that your account is not fully set up yet, or that you have not registered the sender/made necessary checks for the country you are sending to. See the infobip docs for more information.
Full answer by Sara Zorović: https://stackoverflow.stackexchange.com/a/79684433 (CC BY-SA 4.0).
Need it done for your business? UphillTech.