https://blog.canopas.com/golang-interacting-with-google-spreadsheets-b381f819c2eb - append-data

append-data-spreadsheet.go

// https://docs.google.com/spreadsheets/d/<SPREADSHEETID>/edit#gid=<SHEETID>
sheetId := <SHEETID>
spreadsheetId := <SPREADSHEETID>

// Convert sheet ID to sheet name.
response1, err := srv.Spreadsheets.Get(spreadsheetId).Fields("sheets(properties(sheetId,title))").Do()
if err != nil || response1.HTTPStatusCode != 200 {
	log.Error(err)
	return
}

sheetName := ""
for _, v := range response1.Sheets {
	prop := v.Properties
	if prop.SheetId == int64(sheetId) {
		sheetName = prop.Title
		break
	}
}

//Append value to the sheet.
row := &sheets.ValueRange{
	Values: [][]interface{}{{"1", "ABC", "abc@gmail.com"}},
}

response2, err := srv.Spreadsheets.Values.Append(spreadsheetId, sheetName, row).ValueInputOption("USER_ENTERED").InsertDataOption("INSERT_ROWS").Context(ctx).Do()
if err != nil || response2.HTTPStatusCode != 200 {
	log.Error(err)
	return
}