I just imported a file of donations from Engage via the Engage import in which not all of the gifts imported. The first time I tried importing, I received a blank page. The second time, I only included donations associated with the batch number that showed as incomplete when searched for in Civi. I received this message: "413 Request Entity Too Large." I tried again with just the donations I believe to be missing (~10), and still received the previous message.
For reference, I've added the files to Fundraising - Tech - Major Gifts - Engage Import. Please let me know if you have any questions! Thanks.