Find decryption key of coco2d lua

Question

I am trying to find the encryption key for a lua file from a .so file But I am new in this field. I visit websites and found that key is inside xxteaDecrypt function I found two xxteaDecrypt function.

First xxteaDecrypt function

__int64 __fastcall xxtea_decrypt(const unsigned __int8 *a1, unsigned int a2, const unsigned __int8 *a3, size_t a4, unsigned int *a5)
{
  char *v10; // x24
 __int64 v11; // x19

 *a5 = 0;
 if ( a4 > 0xF )
return sub_91716C(a1, a2, a3, a5);
 v10 = (char *)amt_malloc(0x10u);
 memcpy(v10, a3, a4);
 memset(&v10[a4], 0, 16 - a4);
 v11 = sub_91716C(a1, a2, v10, a5);
 amt_free(v10);
 return v11;
}

Second xxteaDecrypt function

__int64 __fastcall encryption::xxteaDecrypt(encryption *this, void *a2, char *a3, const char *a4, unsigned int *a5)
{
  unsigned int v8; // w21
  __int64 result; // x0
  unsigned int v10; // [xsp+4h] [xbp-3Ch] BYREF
  __int64 v11; // [xsp+8h] [xbp-38h]

  v11 = *(_QWORD *)(_ReadStatusReg(ARM64_SYSREG(3, 3, 13, 0, 2)) + 40);
  if ( !a3 )
  {
    __amt_assert(
      "/Users/user/jenkins/workspace/BFG/BFG-android/AMTEngine/native/tools/encryption/encryption.cpp",
      (char *)((unsigned int)&qword_28 + 4),
      "keyExactly16Characters && strlen(keyExactly16Characters) == 16",
      0);
    return 0LL;
  }
  v8 = (unsigned int)a2;
  if ( strlen(a3) != 16LL )
    __amt_assert(
      "/Users/user/jenkins/workspace/BFG/BFG-android/AMTEngine/native/tools/encryption/encryption.cpp",
      (char *)((unsigned int)&qword_28 + 4),
      "keyExactly16Characters && strlen(keyExactly16Characters) == 16",
      0);
  if ( strlen(a3) != 16LL )
    return 0LL;
  v10 = 0;
  result = xxtea_decrypt((const unsigned __int8 *)this, v8, (const unsigned __int8 *)a3, 0x10u, &v10);
  if ( a4 )
    *(_DWORD *)a4 = v10;
  return result;
}

Signature - amta

link of so file - https://mega.nz/file/IKhl1aTY#YAh5SXwLTKuEWZkY1ZO8BCfv9yz-TAN9bW-z6h5PS7M

Please help me to get the key. I am trying from a long time