This may be due to one of the following reasons:

1. The Android smartphone you are using does not support the MTP mode. The smartphone must support the MTP mode in order to connect it by USB cable to the CDJ-2000NXS2. For information on whether or not your smartphone supports the MTP mode and how to set it, see the operating instructions of the smartphone.
2. Depending on the specifications of the MTP mode of the smartphone you are using, the operation may differ depending on whether or not an SD memory card is inserted. In some cases, it may be possible to connect the smartphone to the CDJ-2000NXS2 after removing (or inserting) the SD memory card.
3. Depending on the specifications of the MTP mode of the smartphone you are using, there are some terminals on which the “MTP in use” message is displayed continuously in the foreground of the screen of the smartphone while connected by MTP. With such terminals, rekordbox cannot be operated with MTP connections, so such terminals cannot be connected to the CDJ-2000NXS2 using a USB cable.
4. Depending on the specifications of the MTP mode of the smartphone you are using, MTP connections may only be usable with applications exclusively for Macintosh or Windows. Such terminals cannot be connected to the CDJ-2000NXS2 using a USB cable.