Reproduce Azure DNS REST API long TXT record creation error

rest_test.sh

#!/bin/bash

# exit the script on command errors or unset variables
# http://redsymbol.net/articles/unofficial-bash-strict-mode/
set -euo pipefail
IFS=$'\n\t'

# https://stackoverflow.com/a/246128/295807
readonly script_dir="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"
cd "${script_dir}"

readonly resourceGroupName="B16_repro_long_txt_record"
readonly zoneName="bbkane.com"
readonly recordType="TXT"

get_txt_record() {
    local -r relativeRecordSetName="$1"

    az rest \
        --method get \
        --uri "https://management.azure.com/subscriptions/{subscriptionId}/resourceGroups/$resourceGroupName/providers/Microsoft.Network/dnsZones/$zoneName/$recordType/$relativeRecordSetName?api-version=2018-05-01"

}

make_txt_record_one_value() {
    local -r relativeRecordSetName="$1"
    local -r value="$2"

    cat > "tmp_$relativeRecordSetName.json" << EOF
{
  "properties": {
    "TTL": 3600,
    "TXTRecords": [
      {
        "value": [
          "$value"
        ]
      }
    ]
  }
}
EOF
    az rest \
        --method put \
        --uri "https://management.azure.com/subscriptions/{subscriptionId}/resourceGroups/$resourceGroupName/providers/Microsoft.Network/dnsZones/$zoneName/$recordType/$relativeRecordSetName?api-version=2018-05-01" \
        --body "@tmp_$relativeRecordSetName.json"
}

# works
make_txt_record_one_value not-long-value "$(perl -E "print 'a' x 250")"

# doesn't work - returns Bad Request({"code":"BadRequest","message":"The value 'a...b' for the TXT record is not valid."})  - note that I added ... between a and b for brevity
# make_txt_record_one_value long-value "$(perl -E "print 'a' x 250, b x 250")"

# You can make a TXT record with a value > 255char in the portal (here's me GETting one)
# Also works from dig: dig @ns1-03.azure-dns.com +short long-value-portal.bbkane.com TXT
get_txt_record long-value-portal