How Do I Debug A Large Server Action?

So I have a long Server Action. LIke at least 200 separate action steps.

Then I get an error message like this:

code: 0
file: "C:\Users\anton\Dropbox\workshop-angel\dmxConnectLib\lib\db\Connection.php"
line: 111
message: "Object of class stdClass could not be converted to string"
trace: "#0 [internal function]: exception_error_handler(4096, 'Object of class...', 'C:\\Users\\anton\\...', 111, Array)↵#1 C:\Users\anton\Dropbox\workshop-angel\dmxConnectLib\lib\db\Connection.php(111): PDOStatement->bindParam(6, 'Object', 2)↵#2 C:\Users\anton\Dropbox\workshop-angel\dmxConnectLib\modules\dbupdater.php(38): lib\db\Connection->execute('INSERT INTO `me...', Array, false, 'messages')↵#3 C:\Users\anton\Dropbox\workshop-angel\dmxConnectLib\lib\App.php(174): modules\dbupdater->insert(Object(stdClass), 'create_message')↵#4 C:\Users\anton\Dropbox\workshop-angel\dmxConnectLib\lib\App.php(138): lib\App->execSteps(Object(stdClass))↵#5 C:\Users\anton\Dropbox\workshop-angel\dmxConnectLib\lib\App.php(108): lib\App->execSteps(Array)↵#6 C:\Users\anton\Dropbox\workshop-angel\dmxConnectLib\modules\core.php(92): lib\App->exec(Object(stdClass), true)↵#7 C:\Users\anton\Dropbox\workshop-angel\dmxConnectLib\lib\App.php(174): modules\core->condition(Object(stdClass), '')↵#8 C:\Users\anton\Dropbox\workshop-angel\dmxConnectLib\lib\App.php(138): lib\App->execSteps(Object(stdClass))↵#9 C:\Users\anton\Dropbox\workshop-angel\dmxConnectLib\lib\App.php(108): lib\App->execSteps(Array)↵#10 C:\Users\anton\Dropbox\workshop-angel\dmxConnectLib\lib\App.php(73): lib\App->exec(Object(stdClass))↵#11 C:\Users\anton\Dropbox\workshop-angel\dmxConnect\api\api\send_message_template.php(8): lib\App->define(Object(stdClass))↵#12 {main}"

Which refers to a line number in a file that I’ve never seen…

Does anyone have any tips on how to debug something like this?

My Server Action is send_message_template.php, and the trace has the line send_message_template.php(8). Is this any indication of where to look?