Am I missing something?
Regarding "A Plague Tale Requiem"
Why under Android Phone the price is $27.99 with 30% discount, but under Windows PC the same game with the same 30% discount is $35.25?
Please see the attached pictures.
Can someone please clarify to me?
Thank you!

I'm guessing that GOG can't determine your location properly on the phone, since that's the price for Moldova or Ukraine for example.

What?! Some countries are getting cheaper games? Why is that? If that is the case, It is lame.
I think that is not the case.
The Phone and the PC, which I use, are at the same country and location - Bulgaria.
So my question still stands. Why the different prices on a same product, under different platforms?

Normally, I would say this is a common issue.
However: "normally" stuff tends to be shown more expensive if viewed on a mobile phone.
Has something to do with the thought "if this person can afford a mobile phone, they can afford to pay more"...at least that was the explanation given in a report that I've read years ago.

Now, you say the prices on your mobile are lower than on your desktop pc...no clue as to why, other than what Cavalary said: there might be some inconsistency in your providers.

Is your mobile phone provider the same as your internet provider?

Edit: typo

Edit 2: just thought about another possible explanation:
Are you using a VPN on any of your devices?

In that case, one of your devices may show the European prices in US$ (your PC screenshot), while the other may show the "inside the USA" price in US$ (your mobile screenshot).

That's actually the standard.

GOG tried to avoid it for a couple of years (one world, one price policy), but the publishers insisted.

Also keep in mind that European laws demand that all prices must already include taxes while in other regions taxes are to be added later at checkout.

I assume on one device you are logged in and on the other one you aren't?

US price is $69.99 discounted to $39.89

But that makes no sense.
30% off (which is the discount displayed on the store page) of $69,99 is $48,99 - not $39,89

$39,89 would be 43% off.

So, there seems to be a bigger issue at hand.

You're right, I was looking at the bundle, which is 43% off. The base game is $49.99 discounted to $34.99

Yeah, that's more like it:

US price is $49.99, EU price is $50.37, CIS price is $39.99, so somehow GOG assumes Icosan is in a CIS country when on mobile. Er, yes? You mean you didn't know that. There are even games with dozens of regional prices. Standard industry practice that GOG when it was formed stood against, it was the second clear, specific "pillar" of GOG, on top of DRM-free, "one world, one price". For a short time they were required by court order to implement region checking and regional pricing for The Witcher 2, but they managed to fix that after a while, but then in Feb 2014 they went back on the entire policy, initially saying that for a very small number of highly desired games they'll allow regional pricing (starting with just 3), then in August that year a couple dozen more games started having regional prices, then the floodgates opened and eventually regional pricing appeared for just about every game. For a long time they offered store credit as compensation for those paying more than the base (US) price, but then in February of 2019 they ended that program too. Now there is a smaller difference between EUR and USD, so that standard 1 EUR = 1 USD that's used by publishers makes for small differences, or EU prices may even be slightly lower, and for a while they really were, but there were times when the EU price was a third or so higher, while Russia was typically getting a discount of about 70%, China about 50%, South America and CIS states something similar or more...

Price matrix for A Plague Tale: Requiem, in USD:
Base (US and countries not getting a regional price, includes CN): 49.99
CH: 56.16
GB: 50.66
EU/RS/ME: 50.37
NO: 48.57
CA: 48.29
AU/NZ: 45.35
CIS: 39.99
RU: 32.73
Latin America: 32.28

Regional differences seem lower now than they used to be... At least for this game, highest price is "only" 74% higher than lowest. Remember when it was 4-5 times...

Phone is most likely connecting to a network that's in a different country/location than yours.
I use 4G as my main internet and the network shows me in a state that's 1300 miles away.
Check speedtest.net to see which server it connects you to as the fastest, that's probably where your phone is networking through.

It was much more than that, it was one of the core values of the Good Old GOG.

And not only that, they had only three price points for all games:
free, $4.99, $9.99.
And no DLC or in development games.

Those were the good days indeed. The law also states that the tax percentage should visible in the receipt, but GOG has never shown that anywhere. So technically speaking, GOG does not fully follow those laws.

I also liked the sale strategy - once or twice a year, pretty much the entire catalogue, 50% off.

It was simple and clean. Although I suppose with the trend towards releasing new games, the standardised pricing had to give in the end.

Well, in Europe it's "what you see is what you get". The Price on the product site must be the price you pay in the end. Some keysellers do not follow that rule, they only show the taxes at checkout. But GOG does.

Open this on your phone and in your standard PC browser to see if both show the same location.

And as I already asked: Have you been logged in with the same account on both devices?