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You can learn more about JIRA API and creating JIRA issues using it's API's here: https://developer.atlassian.com/jiradev/apijira-referenceapis/jira-rest-apis/jira-rest-api-tutorials/jira-rest-api-example-create-issue#JIRARESTAPIExample-CreateIssue-Exampleofcreatinganissueusingprojectkeysandfieldnames.
Basically what you see there in "Data" section is something you have to put as IFTTT body. Look at helper functions, which will help you to make some necessary escaping/data transformations: Virtual functions
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