Hey Mark.
1. If you go to admin.microsoft.com, confirm the users have a valid license assigned to them
2. Can you confirm you're able to see an environment when you login to "admin.powerplatform.com"? that would be the environment URL that your colleagues should access.
3. ON the right panel of the environment, you should see a link to "users". Confirm that your colleagues are there. You can follow the steps documented on learn.microsoft.com/.../add-users-to-environment to add users (and similar steps to check they're there).
4. When adding users, ensure that you give them a Security role (sales person, customer service representative, etc) as this is what finally gives them permission to access the data.
Regards
