SN_simple.zip
SN_simple_flat is recognised as invalid here https://github.com/physiomelinks/circulatory_autogen/blob/a726c270fc1f0c1c2a4788e5cd74d57054fd716f/src/generators/CVSCellMLGenerator.py#L179-L182
But it opens and runs fine in legacy opencor (the celml1.1 unflattened version), web opencor (the flat version), and myokit (once converted to myokit model).