Learn Dutch: Veel reizigers hebben dit bij de controle moeten aangeven. - Many travelers have had to declare this at the checkpoint.

This sentence uses the "double infinitive" rule. When a modal verb like moeten is used with another verb (aangeven) in the perfect tense, it doesn't turn into a past participle. Instead, both verbs stay in their full infinitive forms at the end of the sentence.

Why do both verbs go at the very end of the sentence?

In the Dutch perfect tense, the conjugated helping verb (hebben) takes the second position. All other verbs get pushed to the end of the clause. That is why moeten aangeven comes after the rest of the information (dit bij de controle).

Could I change the order of the double infinitive to aangeven moeten?

No, the order is fixed. In a double infinitive, the modal verb (moeten) comes right before the main action verb (aangeven). It helps to remember that it mirrors the English order: "must declare" becomes moeten aangeven.

I remember that aangeven is a separable verb. Why isn't it split up here?

Separable verbs only split when they are the main, conjugated verb in the present or simple past tense. Because aangeven is used as an infinitive here, it stays glued together as one single word.