Applies to: Call2Teams
If you receive a message when login in saying Need admin approval then your Microsoft tenant active directory (AD) has restrictions on your ability to use your Microsoft account for Single Sign On (SSO) to other services.
Call2Teams uses SSO exclusively for portal access so your administrator will need to lift this restriction.
Refer to this MS article for more information on AD consent for SSO:
User access to the Call2Teams portal does not required admin rights on the Office 365 AD account unless you need to make changes to your account with the Sync Now function.