to enable debugging mode :

• from addons > Xenica > configurations Tab , check the 'DEBUG ENABLED' checkbox and save.

• you can see a detailed debug data directly from WHMCS module logging :

first you need to enable module debug logging from: utilities > log > module log , then make sure to “enable debug logging”

• then go back to your admin area or start any action related to xenica that you want to debug,

• you will get some useful info on WHMCS module logging page.

• and more you can notice many error messages (especially Xen Api) on Xenica log file, on this path :

whmcs_path/modules/servers/Xenica/xenica.log

this path can be changed from Xenica configurations Tab

change debug level

for more control on debuging/errors you can edit the debug mode level on Xenica confog file :

WHMCS_path/modules/servers/Xenica/config.php

you will find :

define("xenica_Debug_mode", "2");
/* Debug Mode :
you will need to activate DEBUG_ENABLED first (from Xenica Configurations Tab ).
0 : disable debug/error reporting
1 : log errors to xenica.log file Only.
2 : display errors at the top of page (and log to xenica.log).
3 : display full details and stop execution after the error message (and log to xenica.log). 
*/