Letsencrypt certificates not showing in System->certificates->SSL

I created a certificate using OMV letsencrypt plugin but the generated certificate is not showing under System->Certificates->SSL.
Means, I cannot select this certificate when setting up a server with nginx-Plugin.
What am I doing wrong?
OMV 4.1.14-1, openmediavault-letsencrypt 3.4.5

Solved. I had to re-install letsencrypt plugin and re-create the certificate.
Then it worked ...