open TELEMAC-MASCARET The mathematically superior suite of solvers

I am running a Telemac-2D simulation for a channel confluence with 4 boundaries:

2 inflow boundaries where I've prescribed discharges (455),

1 outflow boundary with a known water level (544),

and 1 outflow boundary where I don't have measured water level data.

To handle the unknown outflow, I attempted to assign a free boundary condition (444). However, the model fails to run and returns the following error:

GIVE A VELOCITY PROFILE
IN THE BOUNDARY CONDITIONS FILE
OR CHECK THE WATER DEPTHS.
OTHER POSSIBLE CAUSE:
SUPERCRITICAL ENTRY WITH FREE DEPTH
IN THIS CASE GIVE A POSITIVE DEPTH
IN THE INITIAL CONDITIONS
OR PRESCRIBE THE DEPTH AT THE ENTRANCE.

My questions are:

What is the recommended way to assign boundary conditions in such a case with two outflows, one of which lacks measured data?

Is it acceptable to use 444 for the unknown outflow, and if so, how should I modify the initial conditions or boundary file to avoid the error?

Any guidance or examples from similar setups would be very helpful.

Thank You.