Purchases less than $25,000 (before tax) do not require review by Procurement Services.
I recommend you have a look at Supporting Documentation, where you will see the documents and processes required based on dollar value and procurement method (informal, invitational, non-competitive etc).
Also, if you haven’t already done so, the FAST videos on creating Purchase Orders are great references: Create PO <$25k, Create PO>$25k.