Sorry for not elaborating.
On help.mikrotik.com, the instruction page says you have to select “I am using the legacy packet (Semtech) forwarder” when registering the gateway at TTN. This gives me an uneasy feeling.
Edit: Found this thread with an answer from you. 
“Semtech Legacy PF still supported (UDP based) by TTN (CE) (aka V3) but other more secure/authenticated options such as BasicStation recommended/prefered…though sometimes its easier to just go with prior default…”
Feels like one day TSN could drop support for the legacy forwarder?