Incorrect spelling


Incorrect spelling, explanation: although it may seem perfectly according to the rule of creating adverbs, however duely is an incorrect spelling, because the adjective due is an exception. Due has silent e, which doesn’t impact the pronunciation of the word and it is there for the word not ending with u. Therefore it is skipped when adding the suffix -ly and the correct form is duly (due plus suffix -ly is duly).

Correct spelling


Correct spelling, explanation: this adverb comes from the adjective due, so it may seem that the spelling should be duely (due plus suffix -ly). However, the correct form is duly; due and true are the exceptions to the rule, because e is silent and it doesn’t change the pronunciation of these words in any way – it is only there for the word not to end with u. Therefore e is skipped when adding the suffix: duly is the correct form.

Definition of duly:
adverb, properly, in an appropriate manner
A duly certified copy of the document is required for the application.
Your request must be duly justified.