'Dead end' error when trying to create floodplain

[Hannah]

Good day SWAT+ community,

I was wondering if anyone has encountered a similar error or knows what could be the cause of it... When I try to create a floodplain during the Delineate Watershed step, I get the following error:

The floodplain I tried to create was using the DEM inversion method, as shown below:

I have created floodplains like this before and did not encounter this error, so I am not sure what has changed this time. I cannot proceed from here and would greatly appreciate any guidance if anyone has advice on what to do.

Thanks in advance and kind regards,

Hannah