在apache worker模式下使用php-zts时找不到mysqli

I have an Apache server running on CentOS which serves a large web request load. Server details:

Server version: Apache/2.2.15 (Unix)
Server built:   Jun 19 2018 15:45:13
Server's Module Magic Number: 20051115:25
Server loaded:  APR 1.3.9, APR-Util 1.3.9
Compiled using: APR 1.3.9, APR-Util 1.3.9
Architecture:   64-bit
Server MPM:     Prefork
  threaded:     no
    forked:     yes (variable process count)
Server compiled with....
 -D APACHE_MPM_DIR="server/mpm/prefork"
 -D APR_HAS_SENDFILE
 -D APR_HAS_MMAP
 -D APR_HAVE_IPV6 (IPv4-mapped addresses enabled)
 -D APR_USE_SYSVSEM_SERIALIZE
 -D APR_USE_PTHREAD_SERIALIZE
 -D APR_HAS_OTHER_CHILD
 -D AP_HAVE_RELIABLE_PIPED_LOGS
 -D DYNAMIC_MODULE_LIMIT=128
 -D HTTPD_ROOT="/etc/httpd"
 -D SUEXEC_BIN="/usr/sbin/suexec"
 -D DEFAULT_PIDLOG="run/httpd.pid"
 -D DEFAULT_SCOREBOARD="logs/apache_runtime_status"
 -D DEFAULT_LOCKFILE="logs/accept.lock"
 -D DEFAULT_ERRORLOG="logs/error_log"
 -D AP_TYPES_CONFIG_FILE="conf/mime.types"
 -D SERVER_CONFIG_FILE="conf/httpd.conf"

Because my server becomes unresponsive when using the fork mode, I switched it to worker mode. First, the php-zts was missing and I installed it.

Then the responsiveness issue was fixed. But PHP is reporting that mysqli is not present. This keeps appearing in the error log.

[Fri Jun 07 14:18:29 2019] [error] [client x.x.x.x] PHP Fatal error:  Class 'mysqli' not found in /var/www/html/.....

Is there anything I need to install when using the PHP-ZTS module? is there any dedicated config which needs to be done?