In order to do mobile checkout from your paybill, you must have enabled mobile checkout on your paybill, learn how to do that from here
To initiate mobile checkout request from your paybill, you will need to provide your paybill number through the provider channel field; otherwise the mobile checkout request will be initiated using our paybill 953055 - meaning that the STK push that will be displayed on the phone screen will display our business name (Africa's Talking) instead of your business name (say Said Catering Services).
The mobile checkout request should look like below, (note the provider channel field)
You can learn more on how to do this, from our docs
Have further questions, email us: firstname.lastname@example.org