Right now, when you hit the max bookmarks per day limit, the only error message you receive is Sorry, an error has occurred.
A more helpful error message is honestly needed here. I would suggest something like what you see for hitting the like limit, preferably with a countdown to the reset.
You have reached the max number of bookmarks for the day. You will be able to add more bookmarks in X hours
Failing the fancier coding, a simpler message warning users have reached the max limit would do the job nicely.