Why SendInput() is not working for enter key on Lock screen?

Question

I'm trying to simulate the "Enter key" using SendInput(), it is working on all the scenario's like SignOut, Restart, Shutdown etc.., except Lock. Here's the code,

INPUT inputs[2] = { 0 };
ZeroMemory(inputs, sizeof(inputs));
inputs[0].type = INPUT_KEYBOARD;
inputs[0].ki.wVk = VK_RETURN;

inputs[1].type = INPUT_KEYBOARD;
inputs[1].ki.wVk = VK_RETURN;
inputs[1].ki.dwFlags = KEYEVENTF_KEYUP;

SendInput(ARRAYSIZE(inputs), inputs, sizeof(INPUT));

my question is, why it is not working on Lock Screen? If this has no way to work, then how can I reach my purpose? Does someone know whats the solution?