Error formatting with trpcExpress.createExpressMiddleware

I'm trying to figure out how to do error formatting but it's unclear how to do it in the context of

trpcExpress.createExpressMiddleware

trpcExpress.createExpressMiddleware

- The documentation use

trpcInit.context().create({ errorFormatter(opts) { ... })

trpcInit.context().create({ errorFormatter(opts) { ... })

which I'm not using as I'm following the React Query example from the docs.

Is there a concrete example I can refer to where should I plug the

errorFormatter(opts)

errorFormatter(opts)