Base64-encoded last 16 bytes of FLH for v4 UID

Author: gmsdelmundo

src/main/java/com/uid2/operator/service/V4TokenUtils.java

@@ -36,7 +36,7 @@ public static byte[] buildAdvertisingIdV4(byte metadata, byte[] firstLevelHash,
 
     public static byte[] generateIV(String salt, byte[] firstLevelHashLast16Bytes, byte metadata, int keyId) {
         String ivBase = salt
-                .concat(Arrays.toString(firstLevelHashLast16Bytes))
+                .concat(EncodingUtils.toBase64String(firstLevelHashLast16Bytes))
                 .concat(Byte.toString(metadata))
                 .concat(String.valueOf(keyId));
         return Arrays.copyOfRange(EncodingUtils.getSha256Bytes(ivBase), 0, IV_LENGTH);