We develop an internal hotel management system, not a platform for third-party customers. Our Meta developer app and WhatsApp business assets belong to the same Business Portfolio. We already use Cloud API directly on one number. We want to onboard a different number currently used in the WhatsApp Business app through Coexistence, preserving mobile app access. Embedded Signup did not offer the expected option to connect the existing Business app account. Requesting advanced permissions prompted us to become a Tech Provider, with an irreversible-action warning. Is self-onboarding through Coexistence officially supported when the same Business Portfolio owns both the developer app and the business being onboarded? Would completing Tech Provider registration enable this, or is an external provider required? Please point us to the applicable official documentation. Direct Support closed our inquiry and referred us here.