Can you still do this? I went to someone's WL and wanted to post a book, but there doesn't seem to be a "post this book" there.
Try clearing your cookies. I have run into a glitch before where the post button goes missing, and this was how I was able to resolve it.
Their account may be on vacation hold or their WL may be on hold.
If their account is on hold, that button disappears and you cannot post to them.
Thank you for your patience