If you are not based in the United States, you should set your spreadsheet to “United States” locale before you run your first upload with BigQuery Uploader for Google Sheets.
The reason is that BigQuery is expecting numbers and dates in US format.
For example, here in Czechia we use “20. 5. 2020” format to say May 20th, 2020. If we tried to upload “20. 5. 2020” as date to BigQuery, the date will fail to be read as date. However, it we switch our spreadsheet to US locale, the date format will change from 20. 5. 2020 to 5/20/2020 and BigQuery will have no trouble reading 5/20/2020 as date and the upload will succeed.
The same principle applies for example to thousand separators – depending on language, the thousand separator can be:
In US English, the thousand separator is comma and that’s what BigQuery is only able to understand.
So the question is: How do you change locale in Google Sheets? Like this: