I am using the Melio account that is internal with QuickBooks Online. 

Thanks for reaching out back to us, BethFL.

I'd be glad to assist you in performing troubleshooting procedures so you can enter an IBAN in QuickBooks Online (QBO) seamlessly.

In some circumstances, excessive cache buildup can result in unexpected behaviors with the product. You can clean this up by logging into your account in a private window. Please refer to these keyboard shortcuts:

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

Once resolved, return to your original browser and clear its cache or switch to a different compatible browser. It could be a temporary issue with QBO or the window you're using. 

Furthermore, QBO allows you to manage your vendors' information. This way, you can access their records and view the progress of their transactions. 

Please don't hesitate to leave a comment below if you have any follow-up concerns about entering IBAN in invoices. I'm always around to help. Stay safe!

How long does it take for the change??

I changed the account but the payment is still going to the old account.

Welcome to the Community, Morgan32. Allow me to share my insights. 

In QuickBooks, the earliest days that it would take to process the changes is two business days. Keep in mind that a federal holiday will add one additional day to the processing of your request. 

For more info regarding vendors, you can check out this article: Pay a Vendor. 

Moreover, you can also enter vendor credits and refunds in QuickBooks Online. 

If you have further concerns, you're always welcome to ask. I'm just one post away.