SMS packages are written in credits. 1 credit is not necessarily 1 sms, because prices for sms differ from country to country and depend on the usd rate exchange; that is why we use credit system. Usually, 1 sms can vary from 0.5 credits to 1.5 credit depending on the country. You can check the prices for sms packages in your admin interface, in Plans&Prices//Additional items//SMS packages.
And here you can see example of prices for sms credits:
Please navigate to Plans&Prices//Additional items in your account to see the exact prices that apply to your system.
Please note! For correct SMS notifications operation, phone numbers should be entered in the system in international format.