You post and match an incoming payment to the incorrect customer account.

Comprehensive and Detailed in Depth Explanation:

Correcting an incorrect payment posting in SAP S/4HANA Cloud involves reversing the erroneous clearing and reprocessing the payment.

Option B (Reset the clearing and reverse the document): Correct. Using the "Reset Cleared Items" function (e.g., via app "Manage Customer Line Items"), you can reset the clearing, then reverse the payment document (FB08 or Fiori app "Reverse Document") and repost it to the correct customer. This is the standard process.

Option A (Change the customer on the payment document): Incorrect. Posted documents cannot be directly edited to change the customer; SAP locks master data fields post-posting.

Option C (Issue a credit memo to the customer): Incorrect. A credit memo addresses overpayments or returns, not misapplied payments.

Option D (Contact the customer through correspondence): Incorrect. This is an operational step, not a system correction method.