For anyone following along at home, this is a bug (in v3.1 beta, generated flashing command is invalid unless there's a factory partition). Nick has reported this on Github:nrcrast wrote:It works if I change the type to factory instead of ota_0, so it seems like there's a bug where it doesn't detect ota_0 as an app area.
https://github.com/espressif/esp-idf/issues/2086
A fix will be avaialable soon.