If your Facebook Business Manager (FBM) review has been waiting for a long time, please submit a ticket to contact Stella Support with a screenshot to check the review status with Facebook. Please login to the Facebook security center ...
You may use two-factor verification to add an extra layer of security to the WhatsApp Business API Client. When you have two-factor verification enabled, any attempt to register your phone number on WhatsApp must be accompanied by the six-digit PIN ...
Please try to fill in all the App info in Setting-Basic and see if the verification is accessible. The App Namespace is the short app name appended to apps.facebook.com (e.g., https://apps.facebook.com/YOUR_APP_NAMESPACE).
If your Instagram Account is using Instagram's professional tools, you can refer here to connect your Facebook Page to your Instagram Business account.
Please check if the WhatsApp number is still in sandbox mode. Stella only allows adding the Two-factor verification (2FA) if the number is live. Please click here to check more details on how to change a sandbox number to a live number.