I have to fix an invoice and re-assign it, but when I try I get a stupid "this will change transactions its linked to" note without a clear understanding what that means?

I appreciate you taking the time to report this to us, Atars.

The message you're seeing, "this will change transactions it's linked to,"  is a warning that appears because the invoice you are editing is connected to another transaction, most likely a payment.

Since you're re-assigning the invoice to a different customer, it means the payment you processed will be unlinked. To make this change, you must first unapply the payment from the original invoice.

To fix this, please go to the payment transaction linked to the invoice and unapply it first. Then, you can edit the invoice to change the customer. After that, you can reapply the payment to the correct invoice.

To assist you in managing your invoices within the program, please take a moment to read this article: Create invoices.

Please feel free to reply if you have additional concerns about your invoices.