Use custom field ID instead of NNNNN in the definition above. Add the updated custom field definition to eazyBI advanced settings or ask the Jira administrator or eazyBI admin to do this for you. eazyBI advanced settings are common for all accounts and only Jira and eazyBI administrators have access to them. After that run an import in the account where this custom field is selected for import as dimension. You should be able to select this custom field for additional data mapping after import.
See the related documentation here: Additional data import into Jira Issues cube