Error uploading Plugin

[Caeppi]

Hello,
when uploading Plugin it does noch work.
I can find following errors in the log and dont no, how to fix it.

{"level":"error","ts":1595849816.1152453,"caller":"mlog/log.go:175","msg":"Encountered an error creating the directory for the new file.","path":"/api/v4/files","request_id":"tkkednze6jfz5pfyziqdjcnekc","ip_addr":"xx.xxx.xxx.xxx","user_id":"abc","method":"POST","err_where":"WriteFile","http_code":500,"err_details":"directory=/var/www/vhosts/...., err=mkdir /var/www/vhosts/xxx/xxx.de: permission denied"}
{"level":"error","ts":1595849848.3035264,"caller":"mlog/log.go:175","msg":"Unable to activate plugin","plugin_id":"com.github.matterpoll.matterpoll","error":"failed to set profile image: failed to set profile image: SetProfileImage: Konnte Profilbild nicht hochladen, "}