Who invented the pre paid postage?

The concept of prepaid postage was invented by the English.

The "Penny Black" is considered the first ever pre-paid postage stamp.

It was introduced by the British for entirely internal use in 1840.

It was called the "Penny Black" because it was black and it cost one penny.

The only design was Queen Victoria's head. Other denominations (and colours) were introduced once the idea caught on internationally.