Hello there, @chanscar. 

Thanks for posting here in the Community. This is a new feature being rolled out by QuickBooks Online (QBO). I recommend opening an incognito browser for your corresponding browser:

• Google Chrome: Ctrl + Shift + N
• Mozilla Firefox: Ctrl + Shift + P
• Safari: Command + Shift + N

Once you're in the incognito window, sign in to your QBO account and try to view the Check Number option on your sales receipt. If you're still unable to see this option, please reach back out to me here. I'm always here to help. Have a safe and productive week ahead!