The following message is from you.
Hello
You are definitively rigth, I'm checking the plugin source code and it currently does not support checkbox control and I'm afraid that when you define a custom field as a checkbox, the plugin cann't handle if the custom field has more than one value. That's because it support controls with only one possible value: dropdown or radio button.
The problem of my test wasn't the form, it was that I don't put more than one value in the Ad custom field. When I put more than one value (it can be done from the form or in the backend directly), here we have the problem.
Unfortunately, this is not a bug, because checkbox is not yet supported. Anyway, this is one of the most popular feature request. So, I think we can include in the next release.
Regards
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ClassiPro Team
Tech Support
alucas@classipro.com