OcSMS and FullTextSearch Class issue

Hi fellows.

First of all thank you for the grate apps! I do really enjoy using’em all.

But never the less I want to fix an issue that is there for a while.

{"Issue while loading Provider: ocsms/OCA\\OcSms\\Provider\\FullTextSearchProvider - OCP\\AppFramework\\QueryException Could not resolve OCA\\OcSms\\Provider\\FullTextSearchProvider! Class OCA\\OcSms\\Provider\\FullTextSearchProvider does not exist"}

This issue occurs in NX 20.0.8 log file as it were in NX 18 and onward. I was unable to solve it with the app maintainer so may be here I can find the solution.

So let’s start from the beginning.

NX 20.0.8 under Debian + NGINX reverse proxy. As I mentioned the story started with NX 18 on the same server.
Elasticsearch 7.10.1
Nginx 1.18.0
PHP 7.4.3
(any additional info needed - please request)

Nextcloud works fine, OcSMS (sms sync) works fine. FullTextSearch does not search and index SMS stored on NX.
The log has the entry from above.

Anyone can help with that?

So what I tryed:
I changed the nextcloud/apps/ocsms/appinfo/index.xml file esp. <provider>OCA\OcSms\Provider\FullTextSearchProvider</provider> along with nextcloud/apps/ocsms/provider/FullTextSearchProvider.php with no result. It seems that the provider name and the file name from provider directory should stay the same. I checked how is it made with other working apps like files or mail and it seems they are using a lib dir with sub-dirs for the class definition.

To be honest I do not understand where the file location is defined, i.e. if I have a Provider definition in info.xml how the system defines or knows where to search for a Class definition? It seems to me that NX just can’t locate the needed file.

My experiments with moving the file and directory around seem to have no effect so I am asking the community for more data regarding the FullTextSearch and how an app should define a class for it and where the file with such definition should be stored.

Thanks in advance!