How to do a label behaviour

Hi ,
I am new to Jira and had a requirement , where i have to get a custom field of type Label and for that field values had to populate values from third party API .Any inputs how it can be done .

  1. Do I need to call API everytime to get the value .
  2. Or any options to get all field values at once and store in a static way .

Have you looked at the “Get Create Issue Meta” endpoint?

Here’s the description:

Returns the meta data for creating issues. This includes the available projects, issue types and fields, including field types and whether or not those fields are required. Projects will not be returned if the user does not have permission to create issues in that project.

The fields in the createmeta correspond to the fields in the create screen for the project/issuetype. Fields not in the screen will not be in the createmeta.