The issue might happen if the URLs are not complete. Check that goCardlessAPIUrl and lexOfficeAPIUrl are full URLs and not just the endpoints in the input.

To troubleshoot easier, I recommend splitting up the API requests you're making in the code and running them one at a time (aka removing all requests you have in the code step apart from the first GET request and testing the step). If it runs correctly, try adding the next and going one at a time to find the problematic one.

You could also look into using Webhook step to make those API requests instead of the code step.