Worth running through this first — about half the time one of these unsticks you, and if it doesn’t, the answers give you the material for a much better question.
Have you actually run it? Under a debugger, with the input you think should work. Static-only analysis produces confident wrong conclusions remarkably often.
Have you checked for anti-debug? If behavior differs between running normally and running under a debugger, that’s your real problem and it’s a different one than you thought you had.
Have you looked at what it does before main? Static initializers, TLS callbacks, constructors. A lot of crackmes hide the interesting work here specifically because people start at main.
Are you sure about the architecture and calling convention? Misreading 32-bit as 64-bit produces plausible-looking nonsense.
Have you re-read the lea instructions? lea doing arithmetic instead of address computation is the single most misread thing in x86. I say this every time because I keep doing it.
Have you tried the dumb approach? Brute force, angr, symbolic execution. Sometimes understanding the algorithm is strictly harder than solving it.
Have you diffed a working input against a failing one? If any input is accepted, the difference in execution path is the whole answer.
If you’ve been through all of this and you’re still stuck, post it — you now have a question people can actually engage with.