I've found out that for countries like United Kingdom, Belgium, Bulgaria, Cyprus, Czech Republic, Estonia, Finland, Greece, Hungary, Iceland, Ireland, Latvia, Liechtenstein, Lithuania, Luxembourg, Malta, Netherlands, Poland, Portugal, Slovakia, and Sweden, music subscription is being operated by Amazon Digital UK, which provides 2 marketplaces: amazon.co.uk and music.amazon.com. Unfortunately the same time Polish default marketplace for Alexa is amazon.com. The Music app requires that Polish music subscribers have their Alexa devices maintained by amazon.co.uk which is not possible if Poland is selected as a current contry region.Well done - as I mentioned, changing your region to USA, for example, is how Alexa users in the UK often switch to be able to access USA features, but the crucial thing after doing that (which I forgot to mention) was to log out of the Alexa app and back in so it redirects it to the USA Alexa. You’ve more or less done the same/reverse to access Uk Alexa.
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Thanks a lot for your support and inspirations.