Air carrier Maintenance Supervisor reported a HAZMAT package was rejected multiple times due to improper processing and incomplete documentation.

Narrative

Person A prepared lithium metal batteries for shipment utilizing the HAZMAT shipping option. Person A used a UN specification box to ship the hazardous materials but covered up the UN markings on the box stating due to no packing group associated with UN 3090; a UN specification box was not needed. The package was rejected by the Company and returned. HAZMAT department was immediately notified and all documentation and pictures were sent. HAZMAT department reviewed the documentation and photos and gave clearance to reship with supervision signature. The HAZMAT was repackaged and shipped but not signed by leadership due to end of day operations for leadership. The package was rejected once again by the Company and returned at which time all documentation and pictures were sent to department immediately. Company cited that UN 3090 shipments must be inside a UN specification box.Suggestions: Possible re-training and reminder to pay attention to all the details provided within the IATA; Dangerous Goods (DG) department; and on the Shipper's Declaration.