So you plan to engage an IT company who supplies a procurement system and with the help of your IT department you will get this on servers and connected up. Haven't you forgotten someone?
Selecting and deploying a procurement system is not just an IT project; it is also a change management project. This system will change the way people work. It will impact them in all sorts of ways, making their job easier in some ways and harder in others. If they don't like some of the items that make life harder they will resist or refuse to use it.
Take a look on the internet. You will see IT system deployment failure statistics vary between 25% and 95%. Whichever of these is true, it is unacceptable. We make sure the stakeholders are identified, engaged and guided through the process so it is "our" system, not "Procurement's" system. The difference is significant.