A data matching issue means the marketplace is not able to verify the information on your application based on the data the marketplace already has for you. To resolve the data matching issue with your application, the marketplace is likely to contact you and ask you to verify your income. You can also do so by uploading documents to the marketplace online or by sending photocopies in the mail. Verifying documents might include a federal or state tax return, a letter of termination, or pay stubs. To determine which documents you need to submit, please consult this guide here.