Can QB on-line record customer/ supplier number? how?

What kind of business do you run? SaaS or else?

Hi there, @frosales-rtacs-n.

I hope you’re having a wonderful day. Let me share some insight about creating duplicates in QuickBooks Online.

When you add another customer, vendor, or employee, you'll get an error message when you use a duplicate name and that you need to enter a different one. Though, it would be awesome to have the option to add a number to your lists. Rest assured that I'll relay this message to our team in concern here on my end and add your vote for this one.

I recommend sharing your thoughts and ideas through your account. Our product development team reviews all the feedback we receive to ensure we’re meeting the needs of our customers. 
 

Here's how:
 

1. Select the Gear icon at the top, then Feedback.
   
2. Enter your comments or product suggestions then select Next.
3. You'll be provided a list of suggested Help articles related to your comment. You can read through them or select Skip and send message.
4. From the drop-down, choose the appropriate category, then select Send message.

Drop me a comment below if you have any other questions about printing forms in QuickBooks Online. I'll be more than happy to help. Wishing you a good one.

I am a CPA and I run a bookkeeping and auditing firm.

I am not sure whether your QBO region supports it or not.

You can utilize the "other number" or "resale number" field for customer and the "account number" or "other number" field for vendor/supplier.