Checkboxes *still* not passing data

Great plugin that’s saved us lots of time! We’re struggling with one thing though: a checkbox field with three checkboxes are not passing any checked box values to Salesforce.

OUR SETUP
The checkbox field asks “Choose your preferred city and date” and lists cities Toronto, Orlando and New York with their respective dates as checkbox options.

WHAT WE’VE DONE
We’ve followed the instructions in the FAQ under “Can I use Salesforce Custom Fields? (Web-to-Lead)” and added an Admin Field Label with the Preferred_c to make it easy to map the checkbox field in the Salesforce Web-to-Lead.

Still doesn’t work.

There was a seemingly obvious solution in this thread posted by “positivelending” but sorry…it is NOT obvious to us. We are trying to figure out where to put the suggested merge field tag (suggestion was “{Input Field:12:value}”) and what the ‘value’ should be: https://ww.wp.xz.cn/support/topic/checkboxes-are-not-passing-data-to-salesforce

Does this mean that, in the Advanced tab, we would check “Allow field to be populated dynamically” and add our field number in this merge tag as “{Input Field:1:value}” in “Parameter Name”? Do we need to change the word “value” to an actual value, or it would automatically add the value(s) checked? If a person checked multiple boxes, would potentially all the values be added and sent to Salesforce?

Any guidance would be VERY much appreciated!