Genesys Cloud - Main

Hi everyone! I am experimenting an unusual error in the Native WhatsApp Integration in Genesys (Genesys as BSP). Sometimes when agents send outbound messages in WhatsApp there appears a caution symbol with the message: "Delivery Error". 

We have the follow answer: 

         "errorPayload": "GeneralError - Failed to send message because this user's phone number is part of an experiment"

Can anyone help me please? This is quite recurrent with random numbers of the client portfolio and we need to solve it quickly. 

Thanks!