# AUR0002 ### **Error message** `yyyy` not registered, did you forget to add @singleton()? ### **Parameters** Name of the key being resolved ### Error explanation A DI container is trying to resolve a key, but there's not a known strategy for it. ### Possible solutions Try adding a strategy for your resolved key. You can do this using `@singleton` or other forms of DI resolution Please also note that this error could be caused by a plugin and not your application. After ruling out that the error is not being caused by your code, try removing any registered plugins one at a time to see if the error resolves itself. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.aurelia.io/~/revisions/NShYVVc01DvYc5bgBiwq/developer-guides/error-messages/0001-to-0015/aur0002.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.