Increasing zabbix_sender log level

[vwr32dbp]

I've seen in other posts on the forums like this one that the zabbix_sender is giving a log line similar to:
"zabbix_sender [7138]: Warning: [line 14] 'Key value' required
zabbix_sender [7139]: DEBUG: answer [{
"response":"success",
"info":"Processed 187 Failed 63 Total 250 Seconds spent 0.001199"}]
info from server: "Processed 187 Failed 63 Total 250 Seconds spent 0.001199"
zabbix_sender [7140]: DEBUG: answer [{
"response":"success",
"info":"Processed 91 Failed 63 Total 154 Seconds spent 0.000763"}]
info from server: "Processed 91 Failed 63 Total 154 Seconds spent 0.000763"
sent: 404; skipped: 1; total: 405"

When I use the -vv flag on my sender command I only get the following lines:
"zabbix_sender [32540]: DEBUG: answer [{
"response":"success",
info from server: "processed: 10; failed: 10; total: 20; seconds spent: 0.005430"
sent: 20; skipped: 0; total: 20"

Notice the first line with a warning message is missing. Is this an option that I have to enable somewhere? I'm trying to troubleshoot trapper items not accepting values via zabbix_sender.

We are on zabbix agent 2.0.2, zabbix server version 2.2.9