beel-es Company Custom Fields API
The invoice custom fields of a company, addressed by `/v1/companies/{company_id}/custom-fields`: labels a company adds to its invoices, such as a store, a project or a cost centre, so that people can see, filter and export them. Each field has a `key` you choose, which never changes, and a list of options: the values already used, per customer or common to every customer. Test and Live keep separate catalogues. Fields and options are never deleted, only archived, and an invoice keeps a copy of the label and value it was saved with, so renaming or archiving never changes an invoice already saved. Custom fields are informational. They are not part of the VeriFactu record sent to the AEAT and do not enter its hash, and no mention the invoicing regulations require can be expressed through them. Use `metadata` for technical identifiers your integration needs and people do not see (order or tenant ids); use custom fields for what a person reads, filters or exports.