If you see the following message when sending your advance VAT return:
Please check your tax number first. Does it exactly match the number you have on file with your tax office?
It is also important that you check your address data. Make sure that the information you've entered under "Settings" > "Business Information" matches exactly the information you have on file with the tax office. Missing or surplus spaces in the address can also cause this error message.
After you have double-checked your information, please try sending the report again.
If you still encounter issues, please let us know.