First of all, there is nothing wrong with your JSON. The problem is with the library Claris are using to parse the JSON, or with their implementation of it.
Now, if you know in advance the path to the value you want, you could do simply something like:
Let ([
myJSON = Substitute ( $json ; "\"52.5\"" ; "\"52§5\"" ) ;
myKey = "putExpDateMap.2021-02-19:46.52§5[0].mark"
] ;
JSONGetElement ( myJSON ; myKey )
)
If you are assembling the path from variables, take care to get the exact path as shown above. Note that the value of the "52.5" key is an array; at least in theory it could conta