In A Taste Of Honey by Shelagh Delaney I found this:
(She wanders around the room searching for fire.) "Where!" she says. She can never see anything till she falls over it. Now where's it got to? I know I saw it here somewhere . . . one of those shilling in the slot affairs; the landlady pointed it out to me as part of the furniture and fittings.
Is it a metaphor? Does it just mean that it is something that costs money or is there a special meaning?
On the Internet I could find different variations where instead of word shilling were used coins, penny, nickle.
Another example from the Internet:
This park stretches over 1,000sqkm from Torquay to Princetown and boasts numerous picnic and barbeque spots. Some are coin-in-the-slot affairs, others are push button and free of charge, while still others are the old-fashioned kind: strictly BYO fuel.