We strongly recommend to ask a professional electrician to install the smart meter inside your fuse box.
If you plan to do it yourself you must use extreme caution. In either case it must be made absolutely sure that there is a main switch directly before the official grid meter in your installation. Ths switch must be disabled (off position) before you do anything.

GRID -> official meter -> main switch -> smart meter DTSU 666 -> fuses of your local grid ------->>>-----
                                                      ||                                         |
                                                      =====================  inverter -----------+
                                                              RS485           +  -     AC 220 V , 1 phase
                                                                              |  |
                                                                              |  |  DC 140 V
                                                                              +  -
                                                                           solar panels

The smart meter must sit directly before the main switch of the fuse box. This means that all energy going into your local grid will flow through the smart meter. Numbers 1,4,7 on the lower side are the three INPUT phases (pointing to the public grid), numbers 3,6,9 on the top side are the OUTPUT phases leading to the fuses of your local grid. 10 (on bottom and on top) ist the neutral wire. Check the wire colors already used inside your grid box. Probably colors like black, brown and gray are used for the three phases and blue for the neutral wire,

Here is a link to manual.
Here is a video which shows how to change the configuration of the smart meter

As shown the password 701 must be entered. Thereafter you can change the settings. Normally this should not be necessary, because the default settings should fit our needs (8 bits, parity N1 , speed 9600 baud , address 4)

The connectors with numbers 24,25 (sometimes also named 22,23) are used for data transmission to the inverter (RS 485). Use the blue/white wire for number 24 (B) and the orange/white wire for connector 25 (A).