You can use the substring function in order to get rid of the unwanted [ ] brackets generated by the JSON aggregator.
How to configure the function:
The function ‘translated’ into words:
From the text (in this case a JSON string), give me only characters 1 till the end of the string minus one character (length -1)
The code to copy:
{{substring(211.JSON String; 1; length(211.JSON String) - 1)}}
Helpful Links:
JSON Guide
