You must have Billing Permissions to correct a claim.
(A7) The claim/encounter has invalid information as specified in the Status details and has been rejected., Status: Entity's contract/member number., Entity: Insured or Subscriber (IL)
What Needs to be Corrected
This means that you may be using the client's old medicare MBI number also known as the Insurance ID number. Here is an article on it: https://www.cms.gov/Outreach-and-Education/Medicare-Learning-Network-MLN/MLNMattersArticles/Downloads/SE18006.pdf
You will need to get the client's new medicare number and update their bill to & Insurance info tab.