What is JotForm?
JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
At JotForm, we want to make sure that you’re getting the online form builder help that you need. Our friendly customer support team is available 24/7.
We believe that if one user has a question, there could be more users who may have the same question. This is why many of our support forum threads are public and available to be searched and viewed. If you’d like help immediately, feel free to search for a similar question, or submit your question or concern.
There are 2 issues here actually - textbox is a HTML field that is intended for a single line only - it should not have additional lines within it.
To use multiple lines in a text, you need TextArea field instead.
If you can give us more details in regards to the condition mark that you would place that should add the new line, we might be able to assist with the same on TextArea, but in general conditions are not the best way to add new lines, cause they could add multiple new lines instead of a single.
Having all that said, once we know more we can give you a more precise answer.