Here's my DMRGateway config that works fine.

This puts Brandmeister on Slot 1 and TGIF on Slot 2.  I recommend you have TGIF on Slot 2 so you can use selfcare since it currently only acts on Slot 2 right now.

The key lines are the 'PassAllTG' lines that mark either slot 1 or slot 2 as the dedicated slot.

[DMR Network 1]
Enabled=1
Address=74.91.114.19
Port=62031
PassAllPC1=1
PassAllTG1=1
Password="passw0rd"
Debug=0
Name=BM_United_States_3102

[DMR Network 3]
Enabled=1
Name=TGIF
Address=tgif.network
Port=62031
Password=passw0rd
Location=0
Debug=0
PassAllPC1=2
PassAllTG1=2