Force online payment on sales

Hi,

I have an onnline shop for kitesurf lessons and we have the option to pay online (paypale/ideal/etc) or cash payment at the start of the lessons.

You will understand that we’d like as much payment in advance, we have some discount when you pay online.

But….

We also have sales/discount at the start and end of the season and then i would like to receive online payments only. So how can i change the products and payments in this way:

Online payment -> is discount
Cash -> no discount possible

https://www.ads-software.com/plugins/woocommerce/