I'm Miles from the Social Care team at Shopify. Thanks for letting us know you're having some issues with PayPal. I'll do my best to help out, but my suggestions below aren't working, I recommend you contact PayPal directly for assistance.
If you're using a dropshipping model, you will be able to download an invoice directly from the supplier. If you're not able to, the next best step is to contact the dropshipper directly and ask for evidence of your purchase.
If you buy your products directly from a supplier and ship yourself, you should be provided with an invoice upon receiving the items. If this is not happening, again, you'll need to contact the supplier directly.
Shopify is generally unable to assist with third-party issues that don't relate directly to any Shopify platform issues. This is because we don't access their systems or policies. In your case, it's generally best to contact them directly for fast and urgent assistance.