You need admin rights to do this
Go here: https://api.n2dmethod.com/settings
Click Users
Click Add User
Give them a username and temporary password
In the dropdown menu, set Role to Client User
Click Save (they will be sent a login email)
On the next screen add their first name and surname
Under User Clients section, in User Client #1 dropdown, select the organisation whose projects you want to give them read-only access to
If you want to let them see another organisation's projects too, repeat the step above for User Client #2 ad User Client #3
Click Save
All done. That user will be able to log in and only see projects from the organisation(s) you are permitting them to see. They won't be able to make changes to the data.