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Typically its on you to do it.
If you claim item not received, PayPal will ask seller to respond with tracking number/proof of delivery. Due to Covid-19 shipping logistics is a nightmare so PayPal may extend the case if necessary. If seller provide proof of delivery, then the system closes case against you.
I suggest you open a case with bbb.org under PayPal San Jose CA to get PayPal Office of Executive Escalations to review the situation. And file a report with ic3.gov if the seller is fraudulent. Scan and Pdf all the info and attach it to the case at bbb.org
This is not for PayPal to do. You are making the claim of fraud on this seller, so you have to do it, bring the evidence to PayPal as above if you haven't already done so.
If the item was shipped, where's the tracking number, if any? See if you can track it with your post office and get an intranet report to see if the package was even addressed to you or any other way of fraud.
If you can't do all of this or PayPal is not budging or there is slow response and you paid by credit card, then try contact your card issuer to dispute the payment.