Hi,
Eventually, with a lot of help from Johnny (Blokada Support), I managed to pay for the subscription for the next 12 months with Bitcoins.
But the road was rocky - this was due to my wallet and my inattention.
I wanted to make it easy and scanned the QR code displayed by Blokada with my wallet app. Already the recipient’s address was entered. Everything was checked and found to be correct. Now quickly sign with the cold wallet and … already the BTC had landed on a “burn address”. Why ? The recipient address was written with capital letters. But according to my wallet provider it has to be written in lower case letters for “bc1” addresses. Then, during signing, it was changed to the “burn address” without my intervention - unfortunately without me paying attention to it.
From Blokada support I got the information that the lower case is not mandatory. Also, they were very accommodating when I successfully implemented the second payment transfer using BTC.
In contrast, my wallet provider has not yet corrected the serious problems for me in his app ! 
Supplementary a note on the transfer fees and minimum transfer limits for cryptocurrencies, especially if you use BTC only occasionally or buy extra for it. Mostly it is then, in relation to the subscription price, but too expensive.
For me, it was an object lesson on paying with cryptocurrencies, which only found a happy ending thanks to the Bloakda team. 
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