Error installing OpenBTS on raspbian for USRP B200

[r00tb3]

I've been following this guide to build and install OpenBTS on raspbian stretch for USRP B200 but I'm stuck at the following error:

# checking for a supported radio type
# - found
# checking for a compatible build host
# - WARNING : dev-tools is currently only tested on Ubuntu 16.04, YMMV. Please open an issue if you've used it successfully on another version of Ubuntu.
#
# adding additional repo tools
dpkg-query: package 'python-software-properties' is not installed and no information is available
Use dpkg --info (= dpkg-deb --info) to examine archive files,
and dpkg --contents (= dpkg-deb --contents) to list their contents.
# - missing python-software-properties, installing dependency
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Package python-software-properties is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
However the following packages replace it:
  software-properties-common

E: Package 'python-software-properties' has no installation candidate
# - ERROR : python-software-properties package was unable to be installed

What does this mean?

What am I doing wrong?

Pls, help ASAP

Regards.