Referencing number input parameter in raster calculator does not work

I have the following parameter-setup for the raster calculator to create the flood_mask based on the number_input_parameter (twi_threshold). For some reason I always get the notification, that the calculation cannot be performed. I tried using the gdal raster calculator too, but there the calculation was not performed at all (result layer = twi_map). When I insert numbers instead of the number_input_parameter, the raster calcultor returns the expected result, thus I am certain that referencing the number_input_parameter does not work. The number_parameter_input is a float with the min value = 0, max value = 15 and default value = 5.

A possible solution that I found was to write a script and save it in the processing toolbox: .

I would help any help solving this issue or suggesting an alternative algorithm apart from the raster calculator to perform the task of creating flood_masks based on an number_input_parameter

extra picture: What is B-G? Aren't usually the layer referenced here?