A toll is not a threat but a budget. It arrives at the opening of act 3 and adds a new question to the puzzle: not just where you go, but in what order.
Behaviour
Entering a node tagged toll costs the number of coins written in the level
data. If you do not have them, that edge counts as closed — the node stays
visible but you cannot walk onto it.
You pay on the first entry, not on every one. Once paid, that node is free for you; coming back through it later costs nothing.
How you read it
A purse sits on the node with a number beside it — and a number needs no translation. Once paid, a seal replaces the purse, so you can look at the board and see which passages you have already bought.
Your coin count sits in the bottom bar.
Taught in
Taught in3-1
A strong tutorial level: remove the rule from the data and the shortest path drops from 15 moves to 7. Collecting the coins is a ten-move detour. The purse and its number read at a glance, so the player understands what to do without having to try it.
Why it belongs in act 3
The third act is dense with one-way edges: bridges, chutes, steep passes. Put a toll on top of that and "the wrong order" acquires a real cost — you can spend your coins on the wrong gate and walk into a route you cannot come back from. This is the act where undo earns its keep.