New contributor question - Send for review

I am new on Pond5. My account has been created long time ago. I am starting to upload some pictures.
I am wondering what it is the process to send pictures for review. The button is grayed among "Cancel", "Save chage" and "Save and send for review". Why the last button is disabled although all mandatory fields are filled-in for my pictures like title, description, keywords (<50) ?

Thanks.