The work is given before anything is returned.
Dāna is often translated as giving or generosity. Here it describes a relationship in which the first 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 pay what you can, a sliding scale or a delayed invoice. The work is given first. Afterwards, if you choose to give, what you offer is received as a gift.