Changing a memory value. C#

OK, I found something that works for writing into the memory:

To use the C/C++ functions I called these parts:
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1. [DllImport("kernel32.dll")]
   
2. 
   public static extern Int32 CloseHandle(IntPtr hObject);
   
3. 
   [DllImport("kernel32.dll")]
   
4. 
   public static extern IntPtr OpenProcess(UInt32 dwDesiredAccess, Int32 bInheritHandle, UInt32 dwProcessId);
   
5. 
   [DllImport("kernel32.dll")]
   
6. 
   public static extern Int32 WriteProcessMemory(IntPtr hProcess, IntPtr lpBaseAddress, uint[] lpBuffer, UInt32 nSize, IntPtr lpNumberOfBytesWritten);
   
7. 
   [DllImport("kernel32.dll")]
   
8. 
   public static extern Int32 ReadProcessMemory(IntPtr hProcess, IntPtr lpBaseAddress, [In, Out] byte[] buffer, UInt32 size, out IntPtr lpNumberOfBytesRead);
   

And I used them as followed:
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1. Process proc = Process.GetCurrentProcess();
   
2. 
   IntPtr procHandle = OpenProcess(0x1F0FFF, 0, (UInt32)proc.Id);
   
3. 
   WriteProcessMemory(procHandle, (IntPtr)0x038C3148, new uint[] { 0x08 }, 4, (IntPtr)0);
   
4. 
   byte[] b = null;
   
5. 
   IntPtr i;
   
6. 
   if((ReadProcessMemory(procHandle, (IntPtr)0x038C3148, b, 4, out i) != 0))
   
7. 
   MessageBox.Show(b.ToString());
   

The writing works (because the money value changes), but I don't get a
messagebox, so the reading doesn't work. What am I doing wrong?
To 0x1F0FFF parameter to open the handle is "enables all possible access rights to the process specified by the Process ID."