Use Crack, Disable antivirus/windows defender before installing the crack.
if you still can't use it with the crack then you will have to buy the key. We all use crack so we don't need keys.
If IDM is important for you then buy it here: https://lkey.info/item/internet-download-manager-lifetime?ref=pcbuilderbd
(they are the official distributor of IDM in Bangladesh ).
If you just need a downloader then I will suggest you use Free Download Manager
, it is free and does not require a key or any money.
Good Luck Mate