You can see what ‘I’ means

The file will be sent to you via the Telegram messenger. It may take up to 1-5 minutes before you receive it.

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The file will be sent to your Kindle account. It may take up to 1–5 minutes before you receive it.

Please note: you need to verify every book you want to send to your Kindle. Check your mailbox for the verification email from Amazon Kindle.