How to send more than 20 messages in 12 hours using the vk API?

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Hello.
1. Log in, getting a token. With access rights to friends, messages and more. other.
2. Send random messages to friends using the application's API.
3. After sending messages to 20 people, it gives an error 7.
What needs to be done to make everything work correctly? As if the application needs to pass information that these users are friends. I read in the friends.areFriends method about the need_sign parameter, which returns "the sign field and allows the server to make sure that the data has not been tampered with on the client.". The sign field contains a unique code of letters and numbers (apparently). This is all great, maybe it needs to be transferred somewhere?