On April 17th 2023, Eir upgraded their mobile voicemail system. This means your personal greeting is not operational since then and needs to be re-recorded.
See below on how to access old messages or re set up your personal greeting;
www.eir.ie
See below on how to access old messages or re set up your personal greeting;

Mobile voicemail migration | eir
On April 17th 2023 we will be migrating customers to a new version of voicemail.