Hi everyone, @magius asked me what the legal implication of vouchers are and i found an internetpage that describe the status of Solidar vouchers very well:
http://www.it-recht-kanzlei.de/agb-gutscheine-verkauf.html
in principle it says:
-When an organization issues vouchers there is a difference if they are sold or give aways.
-If they are give aways -like Solidar- the issuer can freely define the how long they are valid.
-In principle vouchers could be a subsidy for money, like the german wikipedia states in his first sentence: https://de.wikipedia.org/wiki/Gutschein