my server return OK with ALL, but QUERY.test from HOME http://postgis.net return ERROR

hello

I have 4 results from QUERYS in my CentOs 7 + PostgreSQL 13.4 on
x86_64-pc-linux-gnu, compiled by gcc (GCC) 4.8.5 20150623 (Red Hat
4.8.5-44), 64-bit

I connect as USER postgres

QUERY 1:
SELECT PostGIS_Version();
=> 3.1 USE_GEOS=1 USE_PROJ=1 USE_STATS=1

QUERY 2:
SELECT PostGIS_Full_Version();
=> POSTGIS="3.1.4 ded6c34" [EXTENSION] PGSQL="130"
GEOS="3.9.1-CAPI-1.14.2" SFCGAL="1.3.1" PROJ="7.2.1" GDAL="GDAL 3.3.1,
released 2021/06/28" LIBXML="2.9.1" LIBJSON="0.11" TOPOLOGY RASTER

QUERY 3:
SELECT num, street, city, state, zip FROM parse_address('1 Devonshire
Place PH301, Boston, MA 02109');
[num] => 1
[street] => Devonshire Place PH301
[city] => Boston
[state] => MA
[zip] => 02109

now my problem in QUERY 4:
a// I open http://postgis.net/
b// I copy exactly "the command test" from home page:
QUERY = SELECT superhero.name FROM city, superhero WHERE
ST_Contains(city.geom, superhero.geom) AND city.name = 'Gotham';
c// I run QUERY in my server
d// result is:

----------------------------------------------------------------------------------------------------------------------
[pg_last_error()] => ERROR: relation "city" does not exist
LINE 1: SELECT superhero.name FROM city, superhero WHERE ST_Contains...
----------------------------------------------------------------------------------------------------------------------

why this error?
how I can fix?

my target is OTHERS users (not postgres) can use POSTGS
then how can user1, user2, user33 use POSTGIS without connect to DB postgres ??
or... to use POSTGIS is mandatory users connect to postgres DB ?

many thanks