Hello.
As inferred by @fmateo05 it seems your Zoiper config is wrong. Your log says username is john@aio.kazoo.com but this should be john@office-dev.aio.kazoo.com based on your sip config.
Username: john
Hostname: office-dev.aio.kazoo.com
Password: 123456789
Outbound Proxy: aio.kazoo.com (or IP address equivalent)