Tag SurveyMonkey URLs with custom value

I really wish I had seen this before I collected 500 survey responses about our ordering system WITHOUT being able to connect them to an order number.  It turns out you can pass a custom value into the URL of a SurveyMonkey survey:

SurveyMonkey Help Center – Answers

To customize them, create a unique ID ending for each respondent by adding “&c=” at the end of the link followed by the ID number.

EX: &c=00001