Before I get into your question, do you a copy of SAP's document titled 'How to Perform a Year-End Closing in Release 9.1.pdf'? If not, it is suggested reading on the year end process in general. It does have a lot of details that apply to other localizations, so you'd need to skip things that don't seem to make sense. It raises several points that may be helpful. That said it doesn't talk about your specific question.
So here goes:
Reconciling the Sales subledger to the sales accounts in the GL requires some up-front work.
First question: Are you using Advanced GL Account Determination?
Second question: How is your fiscal calendar defined? This is setup in the Posting Periods screen.
Are all sales posted in the same currency?
Do any postings made to the account being reconciled originate from GL Journals or from other sources in the system other than Invoices and Credit Memos? These need to be backed out before comparing the GL balance with the Sales subledger.
Launch the Sales Analysis Report. Here's where the questions above come in, hold on...
You may need to run the report several times if you have multiple Advanced Rules. Each time record the report total and accumulate it if different rules use the same GL Sales Account.
Bottom line - you need to get the output of the Sales Analysis Report to match the way sales are posted to the GL. It gets complex with Advanced Rules. I didn't touch on all the details here, but this gives an outline. Without Advanced Rules it's usually pretty straightforward.
Next you need to get the Accounts postings from GL and compare them to the numbers obtained from the Sales Analysis Report. There're a few ways to do this but the General Ledger report is a good way to start. Launch this report and clear the Business Partner checkbox. Then check the specific revenue account being reconciled. Check the Posting date row and enter the same range of dates that you entered on the Sales Analysis Report. Finally clear the 'Opening Balance for Period' and 'Hide Zero Balanced Acct' settings. Be sure that none of the filters in the Expanded button are set. Run the report.
Again, there's more here than I covered in this outline, but it gives the idea. Alternately you could use the Account Balance screen from the Chart of Accounts drill down, but then be sure to get the Posting Date range correct and clear the 'Display' checkbox.
There's a lot here and I skipped some things. It might be best to reach out to your partner for assistance.