Trouble with "DotNet (Csharp MVC) Example"

[gubin-i-da]

Hello.

I'm trying to solve the problem of integrating ONLYOFFICE (Community Edition) with MS Blazor.
I didn't find any examples that solve this problem on your site.
To understand how integration is supposed to be done for other MS solutions, I used the "DotNet (Csharp MVC) Example" example fom:
https://api.onlyoffice.com/editors/demopreview
.
I deployed the example according to its README.md description.
Of the features of the installation:
and the example and ONLYOFFICE Document Server Community Edition installed on the same machine,
at the same time, ONLYOFFICE Document Server Community Edition had to be installed on a port other than the default port (80),

onlyoffice-documentserver.exe /DS_PORT=8028

because the example is running under iis, which also captures port 80 by default.

After I run the example and try to create a document in it, I get successive two errors:

1. "The document could not be saved. Pleas check connection settings or contact your administrator."
2. "Download failed".

At the same time, on the ONLYOFFICE Document Server, I receive a log (out.log):
nodeJS - postData error: url = http://win-p8l4btor5q4:8028/webeditor.ashx?type=track&fileName=new.xlsx&userAddress=__1; data = {"key":"-1396142706","status":1,"users":["uid-1"],"actions":[{"type":1,"userid":"uid-1"}],"token":"eyJhbGciOiJIUz...."} Error: Error response: statusCode:404; headers:{"server":"nginx","date":"Fri, 16 Dec 2022 14:02:06 GMT","content-type":"text/html; charset=utf-8","transfer-encoding":"chunked","connection":"keep-alive","vary":"Accept-Encoding","content-security-policy":"default-src 'none'","x-content-type-options":"nosniff","content-encoding":"gzip"}; body: Cannot POST /webeditor.ashx at Request._callback (C:\snapshot\server\build\server\Common\sources\utils.js) at Request.callback (C:\snapshot\server\build\server\Common\node_modules\request\request.js:185:22) at Request.emit (events.js:400:28) at Request.<anonymous> (C:\snapshot\server\build\server\Common\node_modules\request\request.js:1154:10) at Request.emit (events.js:400:28) at Gunzip.<anonymous> (C:\snapshot\server\build\server\Common\node_modules\request\request.js:1076:12) at Object.onceWrapper (events.js:519:28) at Gunzip.emit (events.js:400:28) at endReadableNT (internal/streams/readable.js:1333:12) at processTicksAndRejections (internal/process/task_queues.js:82:21)

Found this error description:
https://api.onlyoffice.com/editors/troubleshooting#error0
The document service cannot connect to the document storage editing service at the editorConfig.callbackUrl address.
Check if the Callback handler is working correctly. The document storage service must return {"error": 0} in response.

However, neither in the description of the example nor in the official description
https://helpcenter.onlyoffice.com/en/installation/docs-community-install-windows.aspx
it is not described what else needs to be installed document storage service.
On the pages how it works there is some vague mention that for ONLYOFFICE Document Server Community Edition you can install document storage service and document manager using some software integrators. What it is - I have no idea, and it is not possible to understand this from the sources that are downloaded with empty folders.