Thanks for posting here again about this merge account topic, @JGalarza.

Joining the thread to share further insights on how you can get rid of the error message.

Accounts connected to online banking, can't be merged or deleted. If you're still unable to merge the accounts after disconnecting the bank connection, let's proceed to the next troubleshooting. 

Unexpected issues in QuickBooks are sometimes affected by the amount of data stored in the cache. This is because a regular browser will constantly overwrite itself and will not remove history unless done manually.

Private browsing will not save any history, so it's a great place to identify issues in the browser. Use these keyboard shortcuts to launch a new private window:

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

Try copying the PO one more time. If it works, clear the cache to resolve browser issues in QBO. Using a different browser can also help.

If the same issue persists, I highly recommend that you contact our Support Team directly. This way they can check on your account and escalate the case to our engineers. You can also request a callback so you won't have to wait on the line. See our support hours here.

Here's how to contact us if you're using QuickBooks Online: 

1. Sign in to your QBO account.
2. Click the (?) Help icon in the upper right-hand corner of the Dashboard.
3. Tap the Search tab, then select the Contact Us button and enter your concern in the description box.
4. Once done, select Call us or Get a callback option.

If you have other questions or need further help with this account register merge, just post here again. I'll be right here to help. Have a good one!