Format a string into a json

Hello everyone, i been using 'Ajax Post to URL' and i send this

"[highscore[score][66]]"

but i recieve this json in my server

{"highscore"=>{"score:"=>{"66"=>nil}}}

and i test with postman this json and works perfectly.

{ "highscore": {"score": 66}}

i dont know what to do, i'm read this post but i cannot solve this problem

https://www.construct.net/cl/forum/construct-2/how-do-i-18/post-json-data-with-ajax-objec-62039

please help ;c