Hi, sorry about the inconvenience. We were having a lot of issues with the Google integration so we took it down. We are working with them to get it back online, but I'm not sure of the exact timeframe. In the meantime, the work-around Becky mentioned above is your best option.
They used to have the Google photos option for the custom book but for some reason it's not available anymore... So I just create an album in my Google photos with the photos I want and then download it all into a folder and upload. I wish the Google photos integration was still there. As I said, not sure why it isn't anymore.
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