Giving my 2 weeks notice

Im leaving my sucky pizza delivery driver job and have already sent my gm my 2 weeks notice through text. However, i got no answer, and i was wondering if or how i can write down a 2 weeks notice letter or if i need to. I imagined they need some sort of written proof that i didnt just quit, so i was wondering if someone could help me find out the "formal" way of leaving a 2 weeks notice, or if maybe im just taking the easy way out by sending him a message.

Thanks in advance!

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