I am unable to see any purchase order number options while filling the purchase order, however I notice that the system has given a random number as purchase order number

Hello, useromsaiprints09. I'm here to share some information on how the P.O number works in QuickBooks Online.

When creating a purchase order, QBO sets a number automatically. However, you have an option to enter the P.O number manually. Here's how:

1. Go to the Gear icon and select Account and Settings.
2. Select the Sales tab and go to the Sales form content section.
3. Mark the Custom transaction numbers box.
4. Click on Save and Done. 

You also have the option to add a customised field for the P.O number. Here are the steps:

1. Go back to the Sales form content section.
2. Under Custom fields, enter Purchase Order Number in the Name field.
3. Mark the Internal and Public boxes.
4. Click Save and Done.

To learn how to personalise and add specific info to sales forms, you can check it here: Customise invoices, estimates, and sales receipts in QuickBooks Online.

 You can tag me directly if you have additional questions on this. I'll be sure to get back to you.