Thank you all, the problem was in the project properties. And sorry again for all that I said.

@87922 I think Roblox detects DLL injection and prevents it from loading.

@87922 It works fine with other applications, but not roblox. I don't know if problem is in it.

@nickk No, I entered pid manually, still no errors and no injection.

@nickk Ok, thank you, I will do that and reply later.

@nickk No, I tried rebuilding dll with the Win32 architecture, still doesn't work.
I start Roblox process using this:

RobloxProcess = Process.Start(Path.Combine(RobloxPlayerDirectory, "RobloxPlayerBeta.exe"), "-app");

@91102Yes, it looks like the issue is in the architecture.

@69128Ohh, give me the answer pleease!

@ImmuneLion318 CAn we just forget it please, and you answer the question. I already said that I'm sorry.

@Finity No, it's just a misunderstanding. They aren't "fake programmers" and me either. I understand how the code work, but Roblox blocks dll injection and I don't know how to bypass blocking.

But it work fine with other apps like notepad or google chrome.

@75975 No.

@75975 This didn't work :(
@75975 Of course I will credit. Thank you.

Ok. Sorry everyone, I got mad. No more swearing. I got code from an open source project named Axon. But the code didn't work. So I tried taking code from WRD API. It uses same kernel32 functions but a little other way. It didn't work too. The problem wasn't in the code: I tried exploiting notepad and it worked. The problem was in Roblox. Can you help me, please. Sorry for this again, it's my fault. I didn't describe the problem and was mad.

It doesn't work anyway so answer the question please.