Welcome back to the Wefugees Community and thank you for reaching out to us.
I think the best way to find out, what exactly you need to provide for the marriage is talking to your local registry office ("Standesamt"). We discussed a very similar question here. Please follow the link for more information on this and a potential solution in case you can not provide a certficate of no impediment.
Nevertheless, please also don't hesitate to get back to us if things are not clear or if you have any further questions.
All the best,