Shouldn't the sentence be started with "can you" not "you can" to put "please?" How can I use "please" with a declarative sentence?
"You can" is correct in this sentence. "You can" and "please" here are giving permission and encouraging someone to do an action. Therefore, "you can pet my belly now please" means "you are allowed to pet my belly now, please do it". "Please" here is added for emphasis, this type of sentence is not standard English.
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