Follow these steps to activate you team signup mode:
Click on the name of your workspace in the lateral bar.
Go to Workspace Settings > General.
Scroll down to the section Domain permission.
Type any email domain that you want to whitelist (i.e. that anyone with this email domain will be able to join the workspace automatically. Press Enter.
You can add multiple team domains in this field.
Now, whenever someone signs into Claap with an email included in those domains, they'll be able to join your workspace during their registration.