Use httpie, I couldn't get it right with curl.
http -a admin:${PASS} PUT https://foreman.intert00bz.nl/api/subnets/48 dns_id=4
curl, only for the diehards, I recommend httpie!curl -u "admin:${PASS}" -k -H "Accept:application/json,version=2" -H "Content-Type:application/json" https://foreman/api/domains/25 | jq
curl -u admin:${PASS} -H "Accept: application/json" https://foreman.intert00bz.nl/api/subnets/48
for ID in $(http -a admin:${PASS} GET https://foreman.intert00bz.nl/api/subnets | jq ' .results[] | select(.dns_id == 1) | .id'); do echo ">>> ${ID}"; http -a admin:${PASS} PUT https://foreman.intert00bz.nl/api/subnets/${ID} dns_id=4 ; done