Apostrophe in the content causing nintex workflow to fail. Web request , rest api

{TextStart} and {TextEnd} , what it does? is it Nintex default variable?

And if you try one of these:

1. in stead of using the tags in a build string, use it directly in the rest message. You need to use where you experience the actual string problem. The Build String with these tags will return the same string......These tags are scanned for by the workflow engine, and interpret all characters in between as 1 string, no matter if there are quotes or commas (e.g. if you have a string with a comma, the fn-trim function will see the comma as a separator between 2 function parameters) in there.
2. replace the single quotes with double quotes: 'Title': "{ItemProperty:Title}"
3. fn-replace({ItemProperty:Title},',')
4. use Xml-Encode (or Xml-Decode; I always mix those 2 up)

If you need to encode something in JavaScript then you should use JavaScript functionality for this, which can be found with a simple Google search. If you put your string in double quotes then JS should be able to properly handle apostrophe characters, e.g. var myString = "This is a 'test' text.". URLs can be encoded using encodeURI().