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Premium can be bought on the Patreon page, you can buy any one of the tiers for various benefits described on the tiers.
When you pledge a tier on Patreon, it will join the QuoteBot support server on your behalf and assign a patreon role to you based on what tier you pledged to, Patreon will notify the bot and the bot will add a record of your pledge and give you premium, the bot can only detect your premium if you are in the server, you must stay in the server, or the bot will think your premium pledge was cancelled.
When you purchase premium and the bot makes a record of your purchase, your user id is added to a database along with your subscription tier, when you stop cancel premium your id still remains in the database but the subscription tier is marked as zero, and any server you gave premium to can still see that you purchased it, when you give premium to a server, your user id is put into a database along with the server id.
If you have any concerns, you can ask about this in the QuoteBot support server.