Here is the step to enable and invite your customers, just assume you already get approval from your manager, legal and etc. To invite customer is not just system admin, but users with right permission able to invite their customers to Chatter Group
1. Enable Allow Customer Invitations
Navigate to Setup | Customize | Chatter | Settings
Enable Allow Customer Invitations
2. User permission
Make sure user have Invite Customers To Chatter permission in Profile or Permission Set. Otherwise, user will not see Invite People link
3. Create Chatter Group
Set the group access to Private and enable Allow Customers
4. Member Role
User need to be Manager or Group Owner to able to invite customer. Otherwise, user will not see Add/Remove Members, Change Roles and Invite People link in Chatter Group
5. Invite Customer
User click Invite People link and enter user email address, separate email address by comma for multiple email address.
- Customer will receive email from Chatter and click "Join Now"
- Customer to enter First Name, Last Name, Company Name
- Enter password, confirm password, security question and answer.
- Click Create Account button
If you have validation rule in User object and it cause blocking chatter external user creation, it will throw error message:
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Your support reference number is 1346115889-13737 (1226695017)
Reference: Allowing Users to Invite Customers