Prestashop Datatrans payment module

For one of my client, I was preparing Prestashop eshop with theme - http://promokit.eu/themes/prestashop-1-6-theme-alysum/ (which is nice, I can recommend it, also documentation and support is on good level),
and I was integrating prestahop payment module by https://www.sellxed.com/, which is connected to the datatrans payment system https://www.datatrans.ch/
It is alo nice, but somehow it stopped working in that way, that payment gateways were hidden on the checkout page (technically they were on the page, but hidden by javascript) and I was not able to make it working.
I have searched all the internet, and was preparing to contact their support, then I suddenly noticed, that on the the module configuration page (for example Datatrans VISA)

there is some switch button (Payment Form Position: Use separate page OR Use payment selection page) with description
"The payment form can be displayed directly on payment method list page or on a separate page. In some cases it does not work, when the payment form is displayed on the payment page. In this cases a separate page must be used."

So I tried to change it from default configuration (Use payment selection page) to the "Use separate page" and voila, the payment gateway appeared on the checkout page! Do it with all gateways you want to enable on the checkout page.