The separate pages will need to be merged into a single invoice. This can be done as follows:
On the main document list screen, select the documents which make up the invoice
Click Start
Click the split / join button.
Use the left and right arrow keys to move the green triangle between the separate pages and press the spacebar - this will merge those two pages.
Repeat until all pages have been merged.
Click OK after which the document will be ready for verification - there may be a delay after the merge before the document is actually ready for verification.