Plivo is a pay-as-you-go API platform. Plivo relies on its carrier network to deliver messages successfully. In some cases, messages may be sent by Plivo but not received by users. Plivo charges for messages that are successfully sent from the Plivo platform.
Do I get charged for inbound messages when the message_url or message_method is not specified?
Yes. Inbound messages are free for long codes but are chargeable on toll-free and short code numbers, even without the message_url or message_method configured, when the inbound message state is set as received.