For you

• It hasn't been added. Open the App Library and add it.
• You're at your app limit. Remove an app you don't use, or upgrade. See Plan limits.
• It's admin-only. Client Portal, Autoresponder, Automations, Integrations and Export Data are for owners and admins. Team members don't see them.

For your clients

• The app must be added in the App Library (client-facing apps only).
• A tag on the client may hide it. See client tags.
• Their role may not allow it: billing covers invoices, proposals and contracts; work covers projects, tasks, files and messages.