Zotero cannot resolve doi identifiers anymore

Since today I have an issue with Zotero when using the wizard for importing refrences via an identifier like the DOI number. This has always worked perfectley until today. When using a DOI (which works without any problems on https://dx.doi.org) I get the error of Zotero that it can find the identifier.
I have tried a few times today and first it didn't work, after updating it first seemed to work again but now it doesnt work.
A refrence DOI would be '10.1038/NMAT4581' which doesnt work for me no matter if i add http://dx.doi.org/ before the tag or not.

I'm working on a Windows 10 machine, Zotero version 5.0.76 (latest) I do use the sync function via my account in case that matters.

Thank you very much for your help.
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