The staff member they're trying to add may not have:
an account with Ochre
the school listed correctly on their account.
If they don’t already have one, they need to create a free account. When creating this, they must enter and select the correct school. Once created, they’ll be sent an email with a link to verify their account.
If they already have an account, they need to:
from the top right, select the profile icon, then Edit profile
enter and select the correct school
click Update profile.