This app package’s publisher certificate could not be verified. Contact your system administrator or the app developer to obtain a new app package with verified certificates. The root certificate and all immediate certificates of the signature in the app package must be verified

[Rainman69]

This app package’s publisher certificate could not be verified. Contact your system administrator or the app developer to obtain a new app package with verified certificates. The root certificate and all immediate certificates of the signature in the app package must be verified

[mediaexplorer74]

This app package’s publisher certificate could not be verified. Contact your system administrator or the app developer to obtain a new app package with verified certificates. The root certificate and all immediate certificates of the signature in the app package must be verified

You seems not to be engeneer / developer. :( What's the problem to googling how unlock your Lumia device?!
Easy-Fetch-UWP is OPEN-SOURCE. Download it, delete old certificate file, create new temp. one, deploy app! THATS ALL.

[RoboMWM]

Debug certificate only lasts a year. Would be nice to not have to download and compile source just to get new certificate. I'm assuming if a release version was published, this wouldn't be an issue?

[RoboMWM]

Update: In a previous edit I thought this was resolved, but it is not, that was added by VS when I tried to fix it. I see that there is no LangVersion specified in the csproj for SharpCompress at all. This is a bit offtopic from this issue though, so I created #3

[Empyreal96]

Debug certificate only lasts a year. Would be nice to not have to download and compile source just to get new certificate. I'm assuming if a release version was published, this wouldn't be an issue?

You can repack with Appx Re-sign if you don't wish to rebuild the source code, I haven't had time to resolve the certificate issue sadly

[RoboMWM]

Ah, forgot about appx re-sign. Thank you!