I have the exact same issue. Except I re-joined Ebay Plus after being an Ebay Plus member from May 2023-May 2024. I rejoined June 13th.
When I use any discount code exclusive to only Ebay Plus members, I get the "To apply this code, you need to be an eBay Plus member." Error as you described. This includes my $5 monthly voucher I got sent recently which you need to spend $35 or more. But No, it still fails to work even when meeting all criteria and get the same error as mentioned.
I have reached out to Ebay support more than 5 times and they always tell me they are working on it as high priority. It's been 2 weeks now.
I got 1 response after the first Ebay Support contact advising me that it will be fixed after 72 hours of first sign up and must log off and login again to your account. I've been doing this every 2nd day and still not fixed. Not sure what else to do.
I did find other users with the same issue via another forum (OzBargain) recently and they had same issues but some users appear to have fixed after 2 days of joining Ebay Plus. Some users are able to use the discount codes straight after they sign up. So there is a glitch somewhere.
