Holger had issue installing version 0.4.0 (uploaded by @michielbdejong)
Holger also had same issue installing version 0.4.3 (uploaded by @MahdiBaghbani)
I tried to reproduce the issue and I found a couple of things:
Nextcloud does not store and serve the file in its own infrastructure, instead it serves the file from the URL you put on Nextcloud app upload page! make sure your URL is accessible (ex: use GitHub as file server) and make sure you don't remove the file afterwards, because Nextcloud doesn't store anything.
It takes couple of hours for Nextcloud to propagate new version and signature! be patient.
Holger reported this issue in Gitter.
Holger had issue installing version 0.4.0 (uploaded by @michielbdejong) Holger also had same issue installing version 0.4.3 (uploaded by @MahdiBaghbani)
I tried to reproduce the issue and I found a couple of things:
Thats it, it works now!