Is it possible not to find a payment received on a unique address?

[bitsweet1]

Good evening, I have a problem with a transaction that took place yesterday (at the moment it has 150 confirmations) on an address used only for the transaction itself. The receiver states that he does not know how to recover the bitcoin fraction sent.
In detail: for a purchase made online, I am presented with a screen with the amount in € and btc; I have 10 minutes to do it, but the QR code is not visible, so I try to send the public address to my wallet, but I lose time to calculate the fees to add; the 10 minutes expire, I repeat the operation succeeding in completing it but, I don't realize that in the meantime, the address has changed and, I send the btc to the address that I had saved previously.
Is it possible that the seller is unable to recover the btc from that address?
Thank you in advance for any kind answers
 

[LoyceV]

Is it possible that the seller is unable to recover the btc from that address?

I assume the seller uses a third party payment processor. In that case it's possible the seller can't access the funds, but if that's the case, the payment processor can.
So either you or the seller should contact the payment processor.

[bitmover]

As the address was previously generated, the seller must have the privatekey.

Keep in touch with him and contact his support. Unless you sent it to the wrong address, the seller has control over the funds.

[BitMaxz]

As the address was previously generated, the seller must have the privatekey.

Keep in touch with him and contact his support. Unless you sent it to the wrong address, the seller has control over the funds.

If the seller uses a 3rd party payment gateway like coinpayments or coinbase commerce you can't get the private keys from both of these payment gateways.

Seller's will notified if there is delayed or time-out payment so OP should contact the seller about this issue so that he can also report it to the provider.

If the seller doesn't use 3rd party payment gateway the payment page doesn't have a timer or expiration. So as the OP statement the payment page has countdown timer where the payment address has an expiration time.

[bitsweet1]

I thank everyone for the kind answers. The seller confirms that he has a third party that handles bitcoin payments for him. This is the answer I received today:
thanks for your patience, this is really a matter that must be solved by the BPP

they usually answer within 24 hours

[bitsweet1]

Everything ok, refund received. Thank you very much for your time