Here’s a modern approach to getting your form submissions into Google Sheets. It’ll also (most likely) fix your erroring issue on form submission:
The walk through on that forum post also includes a cloneable for you. To help debug your issue you could always export that and see if it works out-of-the-box on your clients host.
It requires a free Make (Integromat) account but you get to bypass a lot of chaos that some of the older approaches walk you through.
Hope that helps!