An allowlist is the set of approved test phone numbers an unlaunched RBM agent may message. Until the agent is launched, sends to any number outside it are refused.
How it works
Every RCS Business Messaging agent starts in a test state. A developer adds phone numbers as test devices; each device receives an invitation in its messaging app and has to accept it before the agent can reach it. From then on the agent behaves exactly as it will in production for those numbers, rich cards, suggested actions, webhook events, and the sandbox is complete. Sends to numbers that are not on the list return an error rather than being queued.
Why the list exists
It protects consumers from unverified brands. An agent that has not passed Google's and the carriers' review has no verified identity, so it must not appear in anyone's inbox. The allowlist keeps the pre-launch agent to people who chose to receive it, which is also a sensible default for the business: no test message ever goes to a customer by accident.
When it stops applying
At launch, when the agent is approved and enabled on the carriers. After that, reach is governed by consent and by each handset's RCS capability instead. The whole sequence, from brand profile to launch, is described on what an RBM agent is; on SimplyRCS it is filed for you.