This function returns the cPanel account's primary domain.
uapi --output=jsonpretty \ --user=username \ DomainInfo \ primary_domain
{- "apiversion": 3,
- "func": "primary_domain",
- "module": "DomainInfo",
- "result": {
- "data": {
- "primary_domain": "example.com"
}, - "errors": null,
- "messages": null,
- "metadata": {
- "transformed": 1
}, - "status": 1,
- "warnings": null
}
}