Fix WhatsApp Business Certificate Registration -- 2

When I attempt to register my WhatsApp Business number through the Meta Business Manager, the Facebook-issued certificate I downloaded refuses to register—it simply isn’t recognized by the system. Because of that, chat activation between WhatsApp and Meta never completes.

Key facts about my setup:
• The error occurs at the certificate-registration step; no other warnings appear.
• I’m using the official certificate generated inside my approved ad-account manager, not a self-signed or third-party CA file.
• I’m unclear on the exact format Meta expects, so I haven’t been able to double-check SANs, key length, or chain order.

What I need from you is a clear fix—whether that’s adjusting the certificate chain, re-generating it with the correct parameters, or pinpointing any hidden mismatch in Meta’s requirements—so the registration step completes and the number moves to “Connected” status.

Deliverables (all must be met):
1. Certificate registers successfully in Meta Business Manager without errors.
2. WhatsApp chat is activated and a test message can be sent and received.
3. Brief notes outlining what was wrong and the exact steps taken so I can replicate the solution for future numbers.