As-Salaam alaikum,
The Prophet, Sallallahu alaihi Wasallam, said:--

"This world is the prison of the believers and the paradise of the
unbelievers." -[Muslim, Tirmidhi].

Just as penalties of those perpetrating small crimes are delivered locally and serious crimes are sent to the High Courts, so do small errors of believers and close Awliya are punished swiftly and in part in this world, so as to purify them. But the crimes of the people of misguidance are so great... they are referred to the Supreme Tribunal in the eternal realm; mostly they do not receive any punishment here.

Thus in the above Noble Hadith, because the believer receives partial punishment for his faults in this world, it is a dungeon for him, relative to his happiness in the Hereafter. And since the unbelievers will be in Hell and they in part receive their rewards for good works in this world and their large sins are postponed, this world is their Paradise relative to their life in the Hereafter. For in reality and meaning, the believer is also far happier in this world than the Kafir.... because a believer's faith is simply like a paradise in his spirit; while the unbeliever's unbelief (Kufr) sets a fire... sort of Hell.. in his being.