Getting Runtime.MalformedHandlerName - Bad handler when i deploy react app -in netlify

Runtime.MalformedHandlerName: Bad handler
    at _splitHandlerString (file:///var/runtime/index.mjs:900:15)
    at UserFunction.js.module.exports.load (file:///var/runtime/index.mjs:1031:36)
    at start (file:///var/runtime/index.mjs:1195:42)
    at file:///var/runtime/index.mjs:1201:7
    at (node:internal/modules/esm/module_job:194:25)

Hi, I recommend you review the code where the handler name is defined or passed to the runtime. Double-check any variables or inputs that are used to construct the handler name to ensure they are correct. Unfortunately debugging code is outside the realm of support.