curl stopped to post anything

Newline came from these two commands run at the beginning of the script . After

FWK=$(echo $FWK|tr -d '\n') CON=$(echo $CON|tr -d '\n')

it worked ! Appreciate your help a lot

You need quotes around that content inside of the JSON object try and you need to quote the entire string so that spaces inside the variables don't make anything after the space get treated as a separate argument.

echo "{\"WAL-VSX-02\": [\"$TIME\",\"$FWK\",\"$CON\"]}"

The way you had it before there were (single) quotes around several components of the string which works but if there are spaces in any of the vars then the shell parses it as separate strings. This way the whole thing is quoted so the shell will parse it as one string.

To include arbitrary strings in a JSON document, you need to encode the strings as JSON strings properly. This is best done with a utility that understands JSON, such as jq:

#!/bin/bash

while true; do
    fwk=$( top -b -n 1 | awk '/fwk/ { print $9 $NF }' )
    con=$( vsx stat -l | awk '/number/ { print $3 }' )

    printf -v now '%(%T)T' -1

    jq -cn \
        '{ "WAL-VSX-02": $ARGS.positional }' \
        --args "$now" "$fwk" "$con" |
    curl --silent --show-error \
        --json @- 'https://10.199.107.11:8880/test'

    sleep 2
done

In the above code, a JSON document is created using jq. The document will contain a single JSON object with the key WAL-VSX-02. The value of the key will be an array whose elements are the strings listed after --args at the very end of the command.

The JSON object is piped to curl which reads it with --json @-.

To see the posted JSON in each iteration, insert tee as a new pipeline step between jq and curl.

Given the data that I can see in your question, this would generate and post a JSON document equivalent to

{
  "WAL-VSX-02": [
    "12:53:17",
    "8fwk3_dev\n2fwk0_dev",
    "72\n43\n172\n28021\n8261\n14015\n325\n24\n524"
  ]
}

(But on a single line, due to the -c option we use with jq.)

With a tiny bit more effort, we could post those multi-line strings as separate arrays. Just use a slightly modified jq expression that splits the given strings (apart from the first) on newlines:

jq -cn \
    '{ "WAL-VSX-02": ( $ARGS.positional | .[1:] |= map(split("\n")) ) }' \
    --args "$now" "$fwk" "$con"

This would generate the equivalent of

{
   "WAL-VSX-02": [
      "12:53:17",
      [ "8fwk3_dev", "2fwk0_dev" ],
      [ "72", "43", "172", "28021", "8261", "14015", "325", "24", "524" ]
   ]
}