My account here is older than 2020. Your note says the autorization needs to be done manually in this case.

Hello Alan,
Thank you for your question about your account. Please give a description of the problem you are experiencing. Is there an error? It looks like snipes are being placed in your account ok.
Please give a description of the problem you are experiencing and we can take the next step.

In the bid popup, I got the message that I needed to authorize Bidslammer to access eBay. It would not let me enter a bid.
I went back to my account page and followed instructions to fix that but there was no immediate change in the popup.
I then filed a ticket at support and later assumed it was fixed in the meantime since, as you saw, I could then entire a snipe. However, the snipe did not execute since a much cheaper bid from someone else took the lot.

It sounds like you just need(ed) to refresh the Slam-it popup. That page would need to be refreshed manually since it doesn't automatically.
Are you still getting an auth error?