curl --location --request PUT '/rest/api/3/issueLinkType/' \
--header 'Content-Type: application/json' \
--data-raw '{
"inward": "Duplicated by",
"name": "Duplicate",
"outward": "Duplicates"
}'
{"id":"1000","inward":"Duplicated by","name":"Duplicate","outward":"Duplicates","self":"https://your-domain.atlassian.net/rest/api/3/issueLinkType/1000"}