Different methods of payment according to product category

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Hello,
I need to have different methods of payment depending on the category of product.

For now, I've got to modify the code to avoid mixing different types in the car category my products. I have only two categories.

I need depending on the type of category that is in the car, a payment method or another appears.

I think, I'm not sure .... This could be the place?

\ administrator \ components \ com_virtuemart \ models \ paymentmethod.php
public function getPayments

It seems that is where you get the BD payment methods are published.
Would it be possible to access the contents of the cart from getPayments ()? how?

Could you help me find a place to change this?

thanks