In Offer Settings section:
* new invoice details will be available only for new flows, old ones will show old invoice details.
In Flow Settings section:
* if you leave the invoice details field empty, information will be taken from the offer.

* some traffic sources may consider a change of invoice details of a running campaign as substitution of the website.

You can also add contacts to invoice details if needed: email address, phone number, Skype ID or Name.
If you download a landing page to your hosting to change invoice details of a landing page, you should create a flow and add the required data, then, download the landing page linked to the flow. If you do so, invoice details containing in the flow will be added to a landing page.