Requests were fine at first, but now they fail with errors, and you are on the free OpenRouter variants.
The free model variants on OpenRouter or any other LLM cost nothing but are heavily rate limited. They are fine for trying Omni, but daily use hits throttling quickly. This is one of the three usual causes of failed requests, alongside an empty provider balance and a revoked key.
Add a small amount of credit on your OpenRouter dashboard and switch to a paid model, or wait out the throttle. Settings, Overview runs five live checks and detects a selected free model specifically, offering a one-click fix, and Test now sends a real request end to end so you can confirm the fix worked.