Why can't I change the A record in Yandex DNS management using cURL?

Question

Domain Name System

Specify:
curl -H "PddToken: $TOKEN" -d "domain=$DOMAIN&type=A&subdomain=$SUBDOMAIN&ttl=14400&content=$ip" " https://pddimp.yandex.ru/api2/admin/dns/add "
Where:
$TOKEN - the name of the administrator token
$DOMAIN - the name of my domain, delegated and confirmed on Yandex
$SUBDOMAIN - the name of the A record I am editing
$ip - the parameters of the A record being edited
In response, I get:
{"success":"error"," error":"unknown"}
and I don't even understand, but what is actually wrong, I seem to do everything as the Internet tells me

Answer 1

In my opinion, in this case, there is simply no substitution of variables and they are sent as is. You can check with a sniffer.