unable to establish remote connection to mariadb (mysql) on centos7 on gcloud from mac or gscipt

newbie here
- Issue: unable to establish remote connection to mariadb (mysql) on centos7 from a mac or a gscript
- setup: I got 2 lamp machines: one test (107) and another one production (35)
107 - centos6.5 with mysql (vps in digitial ocean)
35 - centos7 with mariadb-server-5.5.52-1.el7.x86_64 (compute engine on gcloud)

db,dbuser,dbpass and port (3306) same on both machines

• problem details:
  I can establish a remote and a jdbc connection to mysql on 107 (test server) from a mac using nc, mysqlworkbench and a gscript app; but when I try to get a connection going with 35 (prod server) with the same user/pass/db parameters I get this response:
  workbench: Can't connect to MySQL server on '35.190.134.164' (60)
  gscript (jdbc connection exception thrown): Failed to establish a database connection. Check connection string, username and password.
  nc on mac: ... (literally nothing after issuing the command nc <35's ip address> 3306

-What I tried:
1. https://mariadb.com/kb/en/library/configuring-mariadb-for-remote-client-access/
my.cnf in 35 looks like this:

[mysqld]
datadir=/var/lib/mysql
socket=/var/lib/mysql/mysql.sock

# Disabling symbolic-links is recommended to prevent assorted security risks
symbolic-links=0

# Settings user and group are ignored when systemd is used.
# If you need to run mysqld under a different user or group,
# customize your systemd unit file for mariadb according to the
# instructions in http://fedoraproject.org/wiki/Systemd



#skip-networking
bind-address = 0.0.0.0


[mysqld_safe]
log-error=/var/log/mariadb/mariadb.log
pid-file=/var/run/mariadb/mariadb.pid

#
# include all files from the config directory
#
!includedir /etc/my.cnf.d

2. firewall-cmd looks like this (for active and public):

trusted (active)
target: ACCEPT
icmp-block-inversion: no
interfaces: eth0
sources:
services: http https

ports: 3306/tcp
protocols:
masquerade: no
forward-ports:
sourceports:
icmp-blocks:
rich rules:
public
target: default
icmp-block-inversion: no

interfaces:
sources:
services: dhcpv6-client http https ssh
ports: 3306/tcp
protocols:
masquerade: no
forward-ports:
sourceports:
icmp-blocks:
rich rules:

3. the dbuser its password is not the issue as I created the same user and password for the same database on both 107 and 35. the user has only usage privileges (select, update, delete, insert) and is set as % on both machines.

I've been on this for 3 days now and I'm not close to figure this out. any help is appreciated. what am I missing?

Thank you.