Hello, i am new user for couchbase, i try install php extension, but i have error

I am try install from this guide
for Ubuntu 18.04

when i checked extension i have this trouble 
PHP Warning:  PHP Startup: Unable to load dynamic library 'couchbase' (tried: /usr/lib/php/20190902/couchbase (/usr/lib/php/20190902/couchbase: cannot open shared object file: No such file or directory), /usr/lib/php/20190902/couchbase.so (/usr/lib/php/20190902/couchbase.so: undefined symbol: json_globals)) in Unknown on line 0

What doing i wrong ?

I fix it, i add in php.ini extension = json. But it enabled. Then i see this message
PHP Warning: Module 'json' already loaded in Unknown on line 0

The page you have referred says that couchbase.so depends on json.so, so you have to load it first.

this is because now you load it twice. To eliminate this message, you can remove the duplicate of json.so which comes after couchbase.so

no dublicate, json enabled default. Maybe him enabled in json.ini ?

i delete json.ini from conf.d . Then work fine.