The French mobile numbers Twilio sells can only be used for Person to Person messaging. This is a country-wide regulatory requirement and recipient carriers will block Application to Person messaging originating from mobile numbers. If your use case requires Application to Person messaging you must use an Alphanumeric Sender ID. Mobile marketing campaigns, pin code verification, etc are considered A2P traffic and must be sent using Alphanumeric Sender IDs.
Messaging traffic is split into two categories in France: Marketing and Transactional. These both require that you use Alphanumeric Sender IDs. Additionally, French mobile networks block Marketing SMS traffic on Sundays, any nights after 10pm and public holidays. If messages are sent during these restricted times, they will be queued and sent out the following day. We also recommend that users have opted into your service before sending them Marketing messages.