Will prayers be answered for someone who repented from taking unlawful money and intended to return it, but does not currently possess the money to return it, despite knowing that theft prevents the answering of prayers?

You must repent sincerely to Allah and resolve never to return to the sin, striving to return any injustices and stolen items. If you are unable to return them, but intend to do so when you are able, then Allah will overlook your shortcomings and accept your repentance, as Allah Almighty says: "So fear Allah as much as you are able," and "Indeed, Allah loves those who repent," and "And it is He who accepts repentance from His servants."