Radiometric Terrain Flattening with S1A SLC data

Hello, there!
I try to run this operator, but I either get the DEM resolution error (Radiometric Terrain Flattening - Hot solve low DEM resolution?)
or with re-grid method unchecked I get “Product without incidence angle tie point grid”.
Prior to RTF I applied the Orbit File, then Radiometric | Calibrate.

I am working on this image:

I work with SNAP 5.0

In the Calibration Step I output to Beta0 band.

SNAP 6.0 has just been released, and something has been fixed for this operator.
Give it a try: