I have the same problem. it doesn’t save the user name and channel ID. Check buttom do nothing. I created a new API key, but the problem doesn’t change. It was working until a few days.
Don’t mind, I’m sure I’m missing something obvious.
I put the shortcode in both, checking all posibilities, with similar result. I understand it should be put in ‘visual’ tab, is it ok?
Also, I have organized my Google Photos images into Albums.