Like most people who tried this, I just have the turn signals first but then the brake light (on the lightbar) would not activate...only the turn signal.
Many vehicles (and all trailers that I know of) have a single wire that has both the turn signal and brake signal going to the tail light. You see that with all trailer harnesses too. Instead, Ram chose to run separate wires for the turn signal and brake lights into the LED tail lights. Those separate signals need to combine in a single wire (well, 2 wires total, but one per side) for the lightbars to work as designed.
Instead of doing this, the easier way is to get that combined brake + turn signal from the trailer harness...and then live with the slight delay.