Run app

[noobchamp]

what I doing wrong?

root@ubuntu:/usr/share/keepass4web# plackup bin/app.psgi --port 8080 --host localhost
String found where operator expected at /usr/share/keepass4web/bin/../lib/KeePass4Web/KeePass.pm line 529, near "request_header 'If-None-Match'"
        (Do you need to predeclare request_header?)
String found where operator expected at /usr/share/keepass4web/bin/../lib/KeePass4Web/KeePass.pm line 556, near "response_header 'Cache-Control'"
        (Do you need to predeclare response_header?)
String found where operator expected at /usr/share/keepass4web/bin/../lib/KeePass4Web/KeePass.pm line 557, near "response_header 'ETag'"
        (Do you need to predeclare response_header?)
Error while loading /usr/share/keepass4web/bin/app.psgi: syntax error at /usr/share/keepass4web/bin/../lib/KeePass4Web/KeePass.pm line 529, near "request_header 'If-None-Match'"
Global symbol "$matchheader" requires explicit package name at /usr/share/keepass4web/bin/../lib/KeePass4Web/KeePass.pm line 530.
Global symbol "$matchheader" requires explicit package name at /usr/share/keepass4web/bin/../lib/KeePass4Web/KeePass.pm line 530.
syntax error at /usr/share/keepass4web/bin/../lib/KeePass4Web/KeePass.pm line 556, near "response_header 'Cache-Control'"
Compilation failed in require at /usr/share/keepass4web/bin/../lib/KeePass4Web.pm line 18.
BEGIN failed--compilation aborted at /usr/share/keepass4web/bin/../lib/KeePass4Web.pm line 18.
Compilation failed in require at /usr/share/keepass4web/bin/app.psgi line 7.
BEGIN failed--compilation aborted at /usr/share/keepass4web/bin/app.psgi line 7.

I thought unloaded modules

[lixmal]

What OS, perl and keepass4web version (or commit) are you using?
Perl version: perl -v
keepass4web version: from package.json or Makefile.PL

All prerequesites installed, also the system ones like libmagic, libkeyutisl, etc.?

Probably an old version of Dancer2, you could try installing the latest version, e.g.
cpanp Dancer2