I have added a class library, and introduced one private method. Invoke looks like:
MethodInfoClass mic = new MethodInfoClass();

const BindingFlags bindingFlags = BindingFlags.InvokeMethod |
								  BindingFlags.Public |
								  BindingFlags.NonPublic |
								  BindingFlags.Static |
								  BindingFlags.Instance;

System.Reflection.MethodInfo privateTestMethod = typeof(MethodInfoClass).GetMethod("PrivateTestMethod", bindingFlags);

if (privateTestMethod is not null)
{
	string returnFromPrivateTestMethod = (string)privateTestMethod.Invoke(mic, null);
	Console.WriteLine($"privateTestMethod: {returnFromPrivateTestMethod}");
}
Example project download from here.