Error message: Data does not match / HMRC failed data checks

When filing a 64-8 form online, you might see the following error message, stating that the data doesn't match.

This usually means that your postcode or National Insurance Number doesn't match that held by HMRC. Before you can file the 64-8, you need to contact HMRC and ask them to update their records.

NOTE: If you get a different error message, contact Support.