[SOLVED]For security reasons, this URL is only accesible using localhost (127.0.0.1) as the hostname

change on

Alias /phppgadmin "/opt/lappstack-5.3.10-0/apps/phppgadmin/htdocs"

<Directory "/opt/lappstack-5.3.10-0/apps/phppgadmin/htdocs">
# AuthType Basic
# AuthName phpPgAdmin
# AuthUserFile "/opt/lappstack-5.3.10-0/apache2/users"
# Require valid-user
Order allow,deny
Allow from all
Satisfy all
ErrorDocument 403 "For security reasons, this URL is only accesible using localhost (127.0.0.1) as the hostname"
</Directory>

works it for me