curl --location --request GET '/rest/api/3/project//securitylevel'
{"levels":[{"description":"Only the reporter and internal staff can see this issue.","id":"100000","name":"Reporter Only","self":"https://your-domain.atlassian.net/rest/api/3/securitylevel/100000"},{"description":"Only internal staff can see this issue.","id":"100001","name":"Staff Only","self":"https://your-domain.atlassian.net/rest/api/3/securitylevel/100001"}]}