The work is given before anything is returned.
Dāna is often translated as giving or generosity. In a dāna place, the six meetings are offered freely and stand complete in themselves.
There is no fee and no expected amount. The six meetings are not an introduction to something you must later buy, and a later gift does not retrospectively purchase the work.
This is not a fee or a delayed invoice. The work is given first. Afterwards, if you choose to give, what you offer is received as a gift.