Thanks for the hint. When submitting from the Organic Maps mobile app, should I just add the "source=Survey on <date>" just in the comments?
Or it is recommended to use other apps/service for adding places. Beginner tutorial mentions only 3 service, but all of them are not really build for use from mobile phone.

So just to be sure I (as newcomer) understand - me being there and adding new parking place myself is not enough, and referencing that parking is indeed there (if there's doubt of my submission) in another mapping is also not adding weight. I hoped that my submission helps someone who is looking for parking area in Meteora.

It's marked as free parking even in Google maps
https://maps.app.goo.gl/9AsSs45qrx6de6eZA?g_st=ic

Whole green area is free parking, entrance from Averof street

Ok, but it is marked as free parking with the sign, and I parked there last night :)