undercharge
un-der-charge
verb
To charge someone less than the correct or expected price for goods or services.
"The shop assistant accidentally undercharged me."
noun
An amount charged that is less than the correct or expected sum.
"There was an undercharge on my bill."
Thesaurus
Antonyms: fleece, gazump, hook, overcharge, pluck, plume, rob, soak, surcharge