HandlerNotFound on Netlify function

Hi there
We copied the repo and deployed it to netlify. In the payment methods function, we get the following error:

{"errorType":"Runtime.HandlerNotFound","errorMessage":"payment-methods.handler
is undefined or not exported","trace":["Runtime.HandlerNotFound:
payment-methods.handler is undefined or not exported"," at
Object.module.exports.load (/var/runtime/UserFunction.js:144:11)"," at
Object.<anonymous>
   (/var/runtime/index.js:43:30)"," at Module._compile
   (internal/modules/cjs/loader.js:999:30)"," at Object.Module._extensions..js
   (internal/modules/cjs/loader.js:1027:10)"," at Module.load
   (internal/modules/cjs/loader.js:863:32)"," at Function.Module._load
   (internal/modules/cjs/loader.js:708:14)"," at Function.executeUserEntryPoint
   [as runMain] (internal/modules/run_main.js:60:12)"," at
   internal/main/run_main_module.js:17:47"]}</anonymous
>

What is wrong? Hope you can help.
Thanks!