When they initially arrived to Russia they paid for quite a lot of offline ads space all around the city and I suppose their ads was there for at least a year. I don't watch TV for last 12 years so have no clue if there was any ads there.

And since back then we already had multiple taxi services (mostly without mobile apps though) with quite low price they likely spend a lot on underbidding them.

I know this comment risks coming off as snarky, but I mean it genuinely: Do you honestly believe the only advertising channels that exist are TV and in person? Is it possible someone on a tech-oriented site is this unaware of the advertising arena?

Lol, I honestly have never seen an ad for Uber in any website I have ever visited. They are, however talked about and recommended by everyone. So I am seriously curious where they are actually advertising.

Some of both but mostly incentives to the drivers and riders, for example new driver bonuses are definitely not profit.