post
https://staging.southparkdata.com/rest/v0/company//documents/
Creates an attachment for a given entity (bill, invoice, transaction, journal entry, or manual journal entry). Pass the entity ID in the URL and the file data in the request body.
Supported entity prefixes: bil_ (bills), inv_ (invoices), txn_ (transactions), je_ (journal entries), mje_ (manual journal entries)
Required scope: Depends on entity type - write:bill, write:invoice, write:transaction, or write:journal