I already have custom code to map tickets to specific JIRA projects based on Domain. But I want to be able to link ticket from ZenDesk to existing issues in JIRA. Here is my incoming sync in JIRA

def remoteDomain = replica.customFields."Domain".value.value
def projectMapping = [
    "accounting":"PANELMEDIA", 
    "android/ios":"MC",
    "android recorder":"MC", 
    "api":"APIE",
    "":"", 
    "":"",
    "":"", 
    "":"",
    "":"", 
    "":"",
    "":"", 
    "":"",
    "":"",
    ]
def domainMapping = [
    "android/ios":"Android/iOS",
    "android recorder":"Android Recorder",
    "api":"API"
    ]
def newProjectKey = projectMapping[remoteDomain]

if(firstSync){
//  issue.projectKey   = "EITP" 
    issue.projectKey = newProjectKey
   // Set type name from source issue, if not found set a default
   issue.typeName     = nodeHelper.getIssueType(replica.type?.name, issue.projectKey)?.name ?: "Bug"
}

issue.summary      = replica.summary
issue.description  = replica.description
issue.comments     = commentHelper.mergeComments(issue, replica)
issue.attachments  = attachmentHelper.mergeAttachments(issue, replica)
issue.labels       = replica.labels

def severityMap = [
"low": "Low", 
"medium": "Medium",
"high" : "High",
"blocker" : "Blocker"
] // ["remote options" : "local option"]
def remoteValue = replica.customFields."Severity".value.value
issue.customFields."Severity".value = severityMap[remoteValue] ?: remoteValue
issue.customFields."Domain".value = domainMapping[remoteDomain] ?: remoteDomain