noun
supplemental ticket; hand-written ticket
A ticket issued manually, often by train station staff, to supplement or replace a regular ticket when the ticket machine cannot issue the desired fare or route.
駅員が補充券を手書きで発行してくれた。
The station staff issued a hand-written supplemental ticket for me.
自動券売機で買えない切符は、窓口で補充券をもらってください。
For tickets that cannot be purchased at the automatic ticket machine, please get a supplemental ticket at the counter.
A boarding ticket; 補充券 can serve as a substitute when a regular 乗車券 cannot be issued.
Compound of 補充 (supplement, replenish) and 券 (ticket). The term likely originated in railway contexts where staff needed to manually issue tickets to supplement machine-issued ones.