I had a play with the Google Spreadsheets API recently to feed in some data from a C# application. The getting started guide is great and I was authenticated and adding dummy data in no time. But as soon as I started to work with real data I got:
"The remote server returned an error: (400) Bad Request."
And digging deeper into the response:
"We're sorry, a server error occurred. Please wait a bit and try reloading your spreadsheet."
The original sample code still worked so it didn't seem like any sort of temporary glitch as the message suggests. After much hair torn it turns out I was getting this error because I had used the literal column names from my spreadsheet. The API expects them to be lower case with spaces removed. If not columns match you get the unhelpful error above, if at least one column matches you get a successful insert with some missing data.
Error messages are one of the hardest parts of an API to get right. If you're not very detailed then what seems obvious to you can leave your developers stumped.
Hope this helps someone else...
(Related: Export Google Fit Daily Steps, Weight and Distance to a Google Sheet; Automate Google PageSpeed Insights and Core Web Vitals Logging with Apps Script; Monitor page index status with Google Sheets, Apps Script and the Google Search Console API)