What is the ruling on taking a sum of money from the municipality in exchange for paying another sum to the pension insurance department? And does planning for one's financial future contradict reliance on Allah?

This type of insurance is forbidden; it is not permissible for a Muslim to voluntarily engage in it. If one is coerced into it, or enters into it out of ignorance, then he is not allowed to take from it more than what he paid into it. He is obligated to dispose of the usurious interest by spending it on the welfare of Muslims or giving it to the poor and needy. He should not benefit from it himself unless he is poor and in need. He should not leave it for the company. Since he has not yet done it, it is not permissible to enter into this contract. Thinking about the future and planning for it financially is permissible and مطلوب (desirable) within the bounds of reality and Islamic law.