For SLES 15.6 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:bjoern_beutel:Aareon/SLES_15.6/home:bjoern_beutel:Aareon.repo
zypper refresh
zypper install proftpd
For SLES 15.5 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:bjoern_beutel:Aareon/SLES_15.5/home:bjoern_beutel:Aareon.repo
zypper refresh
zypper install proftpd
For SLES 12.5 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:bjoern_beutel:Aareon/SLES_12.5/home:bjoern_beutel:Aareon.repo
zypper refresh
zypper install proftpd