Why are my short-duration calls being flagged by the wireless carriers even though my recipients have opted in to receive these calls?
When US carriers see high-volume, short-duration calls at the network level, they can appear to be illegal robocalling. To prevent your legitimate outbound calls from being miscategorized as unwanted or fraudulent calls by the wireless carriers, we highly encourage you to proactively request whitelisting of legitimate outbound calling use cases.
You can request whitelisting for all the major US wireless carriers at Free Caller Registry.