TTB, p.29
Passages: The skills and benefits table includes passages,
or tickets, for travel. They are acquired in blank, and
represent one passage, or trip, between one world and
the next world visited by the starship. They are available in
three forms: high passage, middle passage, and low passage.
Passages may be retained and used as needed, or they may
be cashed in at 90% of their face value
The "acquired in blank" implies a physical token.
IMTU...
they have been a multipart form, of plastic, roughly 20 x 7.5 cm. One's the LS recharge/restock voucher, one's the passenger receipt, one's the ship's receipt, one's the embarking station receipt, one's the disembarking station receipt, and one's the cashout voucher. If the 4 that matter don't all match, they put a fraud notice out on the ship, and the captain has to reimburse the IMoT for the full face value.
So, you agree to a passage on ship X, and go before a boarding agent at the port. You and the ship's rep sign the coupon and fill in the destinations, and the gate agent witnesses. (At smaller ports, he may be the mail scout, or even a part-timer.) He gets the boarding coupon. He sends X-mail to the far end.
The captain gets all but the passenger receipt and the boarding receipt; the passenger gets that and whatever boarding pass the skipper issues.
The skipper then goes to the chandlery, shows the signed off deck to the chandler, and gets one set of food and LS at no cash price. The Chandler gets the fuel ticket, and gets paid by going to the boarding agent.
The skipper then either presents one or more passage coupons for payment of fuel to the collier, or pays cash for fuel. Used ones have the cashout signed over; They get paid to the collier. The rest get a departure note.
Upon arrival, the captain presents the passenger and the coupon to the boarding agent at the destination. The passenger has had to sign that they arrived, that the passage conditions were met (single occupancy, proper access to food, water, and freshers; if high passage, access to a steward with basic laundry and food preparation, as well as entertainment, and at least 30 minutes per day of personal access to the steward.
The agent signs it, takes his copy, and either receives and pays the cashout, or sends the crewman to the bank for the cashout redemption. Either way, he notifies via Xmail the coupons received so as to close out the account.
If the passenger disputes the ticket conditions having been met, both passenger and ship are detained until IMoT and/or the IN and/or IISS have "resolved the situation" - the general rule is that if it was negligence or there is no recording, there is no payment, and the skipper loses his commercial rating (and can't cash passages except at 90%).
If it was lack of proper steward, the captain is permitted to offer a rebate of the difference - if the passenger accepts, the skipper pays 110% of the difference, the passenger gets his 100%, and the ship's transponder is noted as having a steward infraction.
IMTU, there's also a box for passenger accepts double occupancy - but that's a T20ism. (One you can blame me for.)
If you don't have a steward, the boarding agent won't sign off on the High Passage coupon unless the skipper pays the difference ahead of time.
If you bump someone, the boarding agent gets to recover and reissue them a new passage.
All the reports include the passage type, the ship classification and registry, and the name of the steward (if any) and captain. Algorithms in the IISS check these passage notices for overloads and patterns of fraud. It may be slow to grind, but it eventually collates at the sector level way station, and ships over capacity get major trouble.