Advice on use of JOSM import remote command

I am trying to use the JOSM import remote command to pass some osmxml to josm. I want the data to appear in a new layer to be used as visual reference areas in JOSM, rather than as data to be uploaded to OSM, so I am using upload='no'

My osm xml is at this url endpoint: http://tasking-manager-staging.eu-west-1.elasticbeanstalk.com/api/v1/project/1/tasks-as-osm-xml

I am using this url for the remote command:

http://127.0.0.1:8111/import?url=http://tasking-manager-staging.eu-west-1.elasticbeanstalk.com/api/v1/project/1/tasks-as-osm-xml&new_layer=true

JOSM responds with a 200 OK response, but the command seems to have to have no effect in JOSM. I get a flicker of the loading bar, but no sign of the new layer or the data.

Can anyone offer any advice?