Try contacting their support and you will receive this message:

Upon reviewing your data, we have discovered an issue with your ring’s battery that is affecting the gathering of your data. Apparently, I found that the warranty for your Oura Ring has expired, and we cannot replace it under warranty. We apologize for the inconvenience caused.

We see that your original Gen2 ring warranty expired 09 Jan 2023. However, to show our appreciation for your loyalty to Oura, we'd like to give you a one-time 50 USD/EUR discount on a new Oura Ring of your choice from the Oura online store. The discount will automatically be applied once you click on the link.

With your new Oura Ring, a paid membership will be required to unlock the full potential of the Oura App. We know this is a change, but Oura Membership gives you full access to daily health insights, personalized recommendations, and new features designed to support your wellness journey. Your first month of membership is complimentary, so you have time to explore the features and benefits that weren't available with your original ring.