Customers can limit the number of times a user can request a verification code by setting the back-end logic on the client side - which is highly recommended to avoid any potential misuse of the service. TeleSign generally recommends that customers allow up to 3 retries an hour, but ultimately, it depends on the use case. You may get in contact with TeleSign for additional suggestions.
On the TeleSign platform, we do not limit the number of transactions per phone number. This is because we take every request received by customer as a valid request and would not want to prevent potential good users for not receiving their verification codes.