What has typically happened in this scenario is that a user has been created but they have not been added to your organisation or the project. The solution is two-fold:
Add them to your project and/or organisation
Ask helpdesk@makerble.com to make them an Organisation-controlled User (if you are using that feature: Organization-controlled User Accounts)
Steps
Add them to your project and/or organisation
To add them to your project and/or organisation, go back to the Manage Colleagues page
Makerble will have
created a user account for the people you have added.
assigned a Name to each new user based on the part of their email address that exists before the “@” symbol
Therefore search for that user in the Add New Person section by either entering their email address or their Makerble-auto-generated name. They will appear in the search.
Select them.
Select which project(s) you want to add them to
Scroll to the bottom and press Save
Ask helpdesk@makerble.com to make them an Organisation-controlled User
Email helpdesk with their Email Addresses and the name of the organisation