Custom field values keyed by custom field definition ID (UUID) of a definition with entity_type Supplier. Each value matches the definition’s field_type — string for shortText/url, number for number, boolean for boolean, YYYY-MM-DD string for date, or the integer choice id for singleSelect. Keys you send are merged into the stored values — keys you leave out keep their current value. Send null as a key’s value to clear that field, or null in place of the whole object to clear every value. Omit the property to leave all values unchanged. Unknown definition IDs are rejected with a 422.