Each organization you set up in Kinde will have a unique org_code.
If you want users to sign up to a specific organization, the org_code must be passed with their registration request. You need to switch this functionality on per organization.
Go to Organizations and select the organization.
On the Policies page, switch on the option to Allow registrations.
Select Save. Anyone can now register onto this organization if the org_code is passed with the registration request.
If the organization being signed up to is not known when a user signs up, the default organization is used. This applies to users created via API and by import as well.
If you want, you can switch this off to prevent sign-ups to the default org.
Go to Settings > Environment > Policies.
Scroll down and switch off the Sign users up to the default organization if one can’t be detected option.