Own appstore with apps

for testing purpose we setup our own appstore, modified the config to redirekt to ours, copy apps.json and categories.json from the nextcloud app store and extend its content with our own categorie and our own app. So far, our categorie and app is displayed but the installation does not work.
For the app there are two field i did not set yet.

#1->certificate “… string”
#1->releases->#2->signature-> “…string”

Are this field mandatory and how to get the certificate and signature for my own app in my appstore?

Thank you,

Nobody have experiences writing and publish apps?

This forum is mostly targeted for users.
See the dev category for developer related postings.

Another resource to contact will be https://cloud.nextcloud.com/call/xs25tz5y