Handling Purchase Confirmations and VAT for Domestic Conversion of Export Goods

We are planning to use a portion of the products originally manufactured for export for domestic purposes, and I am wondering if any separate tax measures, such as VAT adjustments, are required. Our business model involves purchasing products manufactured by Manufacturer A and exporting them. At Manufacturer A's request, we recently issued and provided a Purchase Confirmation. However, since exporting the entire quantity has become difficult, we are considering a plan to use part of the volume domestically. 1. Are there any legal or tax standards regarding the timeframe within which the export must be completed after the issuance of the Purchase Confirmation? 2. If we export a portion and convert the rest to domestic sales, are there any specific actions that our company or Manufacturer A must take? 3. How should tax invoices issued at the zero tax rate be handled, and will there be issues regarding the additional reporting of VAT?