An error occurred: Failed to process your item. Please specify background subsection of app section in the manifest.

[AMT]

Hi, Chrome Web Store Devs

We had our item uploaded as packaged app by mistake, and now remade it as a hosted app. Though when trying to upload it gives an error:
An error occurred: Failed to process your item.

Please specify background subsection of app section in the manifest.

While if we try to create a new app - it uploads successfully. The problem is - our existing app is available for all devices, while all new apps are restricted to Chrome OS. 
We would want any help with switching the existing packaged to a hosted app as soon as possible.

We have added Google SSO and payments, would be great to get any support from the Google team to make our product available to users!

Thanks guys! 
P.S. seen a number of similar topics, but didn't find an answer.