If you'd like to allow customers to set their own ticket price, select "Enable pay-what-you-can virtual unlocks" when creating a ticket bucket for your virtual screening:

Set a default price to appear in the checkout window by adding a price in the "Default Price" section of the ticket bucket:

And specify the minimum price they can pay - or leave it $0 - in the ticket bucket settings:

Audience members will be able to drag the slider or type a number to choose their ticket price in the checkout window:

NOTE: There is no "donation at checkout" option with pay-what-you-can tickets.