'No function clause matching' occurs when none of the function definitions match the arguments provided. Review the function's clauses to ensure they correctly handle the input types and patterns being passed.

'No function clause matching' is a common error encountered in Elixir that indicates that a function was called with arguments that do not match any of its defined clauses. In Elixir, functions can be defined with multiple clauses, each designed to handle different types of inputs or patterns. When this error occurs, it usually means that the arguments you provided do not satisfy any of the patterns specified in the function's clauses. To troubleshoot this issue, start by examining the function definition. Review each clause carefully to ensure that they account for the types and structures of the inputs you are passing. This may involve checking for any unexpected data types, such as strings instead of integers, or mismatched arities where the wrong number of arguments is supplied. You can also use pattern matching in your function definitions to handle specific cases, which can help make your code more robust. If your function is expected to handle a variety of inputs, consider adding a catch-all clause using the _ pattern to capture any unmatched cases and provide a default response or error message. Finally, if your function relies on other functions, ensure that those functions return the expected outputs, as incorrect outputs can lead to mismatched clauses. By systematically reviewing your function definitions and inputs, you can resolve 'no function clause matching' errors and improve the reliability of your Elixir application.