4A. Coastal DEM Processing -- ouput DEM parameter type

In 4A, Coastal DEM Processing, the input parameter when using the toolbox named "Output DEM" seems to be requesting an existing raster, rather than a string to use for the output file name. If a string is entered, the Geoprocessing panel gives an error "ERROR 000732 Output DEM: Dataset dem does not exist or is not supported." If I select an existing raster dataset, the error goes away and it would let me run the tool; however, using an existing raster dataset as the input for the "Output DEM" name parameter wouldn't work. The python code itself is OK. When manually entered in the GIS Python window, the script worked perfectly.

ArcGIS Pro 2.6.0
StreamStatsDataPrepTools version downloaded 8/14/2020.