Pasted this in terminal;
URL='https://www.dynu.com/support/downloadfile/31'; FILE=`mktemp`; wget "$URL" -qO $FILE && sudo dpkg -i $FILE;

but instead of installing its shows this error;

Selecting previously unselected package dynuiuc.
(Reading database ... 203194 files and directories currently installed.)
Preparing to unpack /tmp/tmp.mWPY90SSl2 ...
Failed to stop dynuiuc.service: Unit dynuiuc.service not loaded.
dpkg: error processing archive /tmp/tmp.mWPY90SSl2 (--install):
subprocess new pre-installation script returned error exit status 5
Errors were encountered while processing:
/tmp/tmp.mWPY90SSl2

note;
also tryed this with root

got the same error.

still no solution?

I unpacked the package, modified the preinst script, rebuilt the package, and reinstalled it.

dpkg-deb --extract 31.deb mydynuiuc

dpkg-deb --control 31.deb mydynuiuc/DEBIAN

modify mydynuiuc/DEBIAN/preinst

chmod 755 mydynuiuc/DEBIAN/*

dpkg-deb --build mydynuiuc

dpkg -i mydynuiuc.deb