BrainPop - Your Google Account has not been registered by your Google Domain Administrator. Please contact the admin or a teacher to list you, and then log in again.
Teachers can complete their account setup by logging in to BrainPOP via Google. Then they can finish setting up their students by importing classes from Google Classroom or having students join with a Class Code. Below is a link to an article how to setup your classroom.
https://help.brainpop.com/hc/en-us/articles/360045444831