What is the problem? Please be detailed.
I got an HTTP Status 400 – Bad Request when uploading a form to ODK aggregate sandbox server (https://sandbox.aggregate.opendatakit.org/).
I have tested the uploaded form using ODK validate v1.11.0. and it says that the Xform is valid.
Attached is the form
TestForm1.xml (29.3 KB)
Here is the screenshot of the error on the sandbox server: