QXL Online is no longer connected to QuickBooks Online.  Your user token is no longer valid.

How to connect/reconnect QXL Online

Refer: How to download and Install QXL Online

After installation, You may notice following icons over the desktop.

First use of QXL Online

First, make sure you have access to QuickBooks Online company file with Administrator privileges, to authorize QXL Online to connect to your QuickBooks Online Company file. 

In case you are using QuickBooks Online Accountant (a ProAdvisor) that you need to be logged in to “Your Books” (the option in the left menu bar for accountants) or the client’s books.

To authorize QXL Online to connect to your QuickBooks Online Company file just click the Red/Green toggle button.

QXL Online connection wizard should appear. Enter a Connection name to identify which account this represents, then click "Connect to QuickBooks".

QXL Online will QuickBooks Online authorization page on your default browser. Click "OK" to authorize QXL Online at QuickBooks Online.

Click on "Connect to QuickBooks" to begin authorization process. (For QXL-Online v18.0.0.025 or lower). For QXL-Online v18.0.0.026 and above, This step will be skipped and you will be prompted with QuickBooks credentials.

By clicking "Authorize QXL Online to Connect to your QuickBooks Online" open authorization screen. You need to authorize your company file to work with QXL Online.
You need to enable popup from your browser.

Enter your QuickBooks User ID & Password, then click "Sign In".

For QuickBooks Online Simple Start/Essentials/Plus Account

Select company file which you want to use with QXL Online. If you have multiple company files.

For ProAdvisor Account

Select "Company/Firm" from the list. Click "Add app to firm"

After selecting the company, please click the "Authorize" button. It will allow "QXL for QuickBooks Online" to access your QuickBooks Online company data file.

After successful authorization, it will return back to QXL Online page as connected status. You can close this window.

QXL Online is successfully connected to your QuickBooks Online company. Click "OK" & "Close" to complete configuration.

Switch back to QXL Online and click Export Data

After the export is completed. Exported data folder will open. Exported data placed at below location by default:

C:\Users\User Name\Documents\QXL\Company FileName Folder

QXL Online Features:

1. Export QuickBooks Online Data to Excel format.

2. Export QuickBooks Online Data to CSV format.

3. Export QuickBooks Online Data to SQL Server.

4. Choose export file(s) location.

5. Export to Separate files or a single file.

6. Export all tables, selected tables or excluded tables.

7. Custom Query Export.

Also, Refer:
QXL Online options and settings