Hi afit2,
Thank you for your post.
According to your description, I understand that you have purchased the Exchange Online Plan 1 for your users, however, there is no order number in the printable invoice page. If there is any misunderstanding, please feel free to post.
Generally, the order ID will be displayed under the Invoice No in the Invoice file like the following picture show.
However,
for a clear view about this issue, could you please paste the screenshots both
about the printable invoice page and editable detailed page you mentioned in the original post?
To request the screenshots, I have sent a private message with a subject of <Purchase orders don't show on printable invoices> to you in case it contain some privacy of yours.
To access the private message:
-Go to the Your details section on the right side of the community site.
-Click Private messages.
-Click the subject title of the response to read the message
In addition, since this issue is more related to Sales and Billing, you may also contact our Sales and Billing support team for such issue for more detailed information by following the links below:
Office 365 for Enterprise:
http://onlinehelp.microsoft.com/en-us/office365-enterprises/ff652548.aspx
Office 365 for Professional and Small Business
http://onlinehelp.microsoft.com/en-us/office365-smallbusinesses/ff652569.aspx
Thanks,
Jolin Qiao