How it works

1. Calls /ark/router with body fields client_id, data_type=JSON, resourceToken, timestamp, type=bg.clearance.invoice.get and calculated sign.
2. Downloads file from returned URL using headers toa-app-key, toa-random, toa-timestamp, toa-sign.

Timestamps are generated in Oman timezone (Asia/Muscat). Files are zipped before download.