Hi,
If anyone else other than me needs a BMS cable from mpp solar pip5048 gk to pylontech us3000c here is the pinout connections which worked for me:
3 - 8
5 - 7
7 - 5
8 - 3
The numbering is standard for RJ45, you can find in this discussion thread pictures with the connections to other inverter & battery combinations where you have a very explicit diagram of the RJ45 numbering. If you don't like to scroll just keep in mind that numbering starts with 1 from left to right with the connector having the clip on the table and the hole where the cable enters towards you.