After "due to," you should typically put a noun or a noun phrase. "Due to" is a prepositional phrase that functions as an adjective, and it needs to modify a noun in the sentence. Here are some correct examples:

Correct: The flight was delayed due to bad weather.

Correct: The cancellation of the event was due to unforeseen circumstances.

Correct: The decline in sales was due to increased competition.

In each of these examples, the phrase "due to" is followed by a noun or a noun phrase that explains the cause of the situation described in the sentence.

Incorrect usage:

The project's failure was due to didn't meet the requirements.

The delay was due to arrived late.

In these incorrect examples, "due to" is not followed by a noun or a proper noun phrase, leading to incorrect sentence structure.