Restrictions of Viber chatbots

1. Sessions. A session is a 24-hour time window that is activated by a subscriber of the chatbot when they send their first message within the chatbot. The session automatically ends after 24 hours. The next session will be activated as soon as the chatbot subscriber sends a new message.
2. Restriction on the number of free messages per month. To engage in conversations with their subscribers, the chatbot owner can send messages initiated by the chatbot. Chatbot owners will be charged for messages sent beyond 10,000 messages initiated by the chatbot sent each calendar month. Once this limit is reached, Viber will block the sending of new free messages initiated by the chatbot until the next month. All messages sent by the chatbot owner outside the free 10,000 messages/month will be billed according to Viber's current price list.
3. Subscription to a chatbot. To be able to interact with a Viber chatbot, the user must be its subscriber.
4. Restriction on media file sizes. Viber limits the sizes of media files that can be sent through its API.

   Images	Maximum image size: 1 MB on iOS; 3 MB on Android. Extension: jpeg, png or gif. More information here.
   Video	Maximum size 26 MB. Only MP4 and H264 are supported. More information here.
   File	Maximum size 50 MB. More information here.

5. Restrictions on data processing. Viber requires all applications using Viber API to comply with their data privacy and security policy and process data in accordance with the law.
6. Restrictions on bot usage. Viber prohibits the use of bots that may violate their terms of service, such as bots that spam or create unpleasant experiences for users. More information about acceptable use policy can be found here.
7. Restrictions on message size. Viber limits the size of messages that can be sent through the API. The maximum size of a message is 7000 characters. More information about Restrictions can be found here.
8. Restrictions on button size. The keyboard is divided into 6 columns. Each button has a width of 1 to 6 columns. The client will display the buttons in the order they were sent and fit as many buttons as possible in each row. Keyboards can contain up to 24 rows. The label on the button can be up to 250 characters long. If the text is too long to display on the button, it will be truncated and end with "...". More information can be found here.
9. Restrictions on supported options. Viber does not support email options (the user's email address is sent as a contact when a button is pressed) and clear options (the option allows for clearing the current user keyboard of postback buttons).

These restrictions are in place to ensure the safety and quality of the services provided by Viber. Additionally, they may be subject to change in accordance with Viber's policies.