IF MAC = "" string s1 : if Mac = "" s2?

the original code was just

while (MAC.ToLower().StartsWith("000b82"))
{
  string s = x98c0d0f014f8bfe2 + "&gnkey=0b82";
}

What this does is takes and verifies the MAC address then creates a a hashkey. I need it to be able to take new MAC addresses beginning with c074ad and do "&gnkey=c074" if c074ad is used or do &gnkey=0b82 if 000b82 is used.

What am I missing? c074ad is new MAC. https://github.com/SH4ZB0T/Grandstream-Provisioning-Tool/tree/master/GrandstreamProvisioningTool/dll/Grandstream

// Token: 0x06000006 RID: 6 RVA: 0x00002178 File Offset: 0x00000378
    public static byte[] Encode(string inputStream, string MAC, bool encryption)
    {
        if (MAC.Length != 12)
        {
            throw new Exception("Mac Address must be exactly 12 characters long.");
        }
        if ((!MAC.ToLower().StartsWith("000b82")) || (!MAC.ToLower().StartsWith("c074ad")));
        {
            throw new Exception("Unrecognized Device");
        }
        TextEncoder.xdb0ee97a9934cea1(inputStream);
        string x98c0d0f014f8bfe = TextEncoder.x037d2dea37c72401();
        return TextEncoder.x875a866de1bf2e29(MAC, x98c0d0f014f8bfe, encryption);
    }

    // Token: 0x06000007 RID: 7 RVA: 0x000021E0 File Offset: 0x000003E0
    private static byte[] x875a866de1bf2e29(string x61f6b464f047216f, string x98c0d0f014f8bfe2, bool xa2cf66bde80e30c9)
    {
    ->  if ("000b82") {string s1 = x98c0d0f014f8bfe2 + "&gnkey=0b82"};
    ->  if ("c074ad") {string s2 = x98c0d0f014f8bfe2 + "&gnkey=c074"};
        int num;
        if (((uint)num & 0U) != 0U)

The || in the second conditional should be &&, or there should only be one negation (!), with both of the condition in parentheses.

So either

if ( !(MAC.ToLower().StartsWith("000b82") || MAC.ToLower().StartsWith("c074ad")))

or

if ( !MAC.ToLower().StartsWith("000b82")) && !MAC.ToLower().StartsWith("c074ad"))

As it is, the condition is always true, no matter what the MAC is.