How do I recover missing numbers on my Apple Gift Card?

Please follow the steps in this Apple Support article. 

If you can't redeem your Apple Gift Card or App Store & iTunes Gift Card - Apple Support

If after reviewing the article, and following the directions in the article, you need additional assistance please follow the link below to contact official Apple Support. 

Contact Apple Gift Card Support

If you receive a request for payment using Apple Cash, or If you believe you are the victim of a scam, please contact Apple Support and report it to local law enforcement.

You may also report the scam to the FTC Complaint Assistant and to the FBI’s Internet Crime Complaint Center

If you receive a request for payment using Apple Cash, or If you believe you are the victim of a scam, please contact Apple Support and report it to local law enforcement.

Click here and ask Apple Support for assistance; supply them with the remaining part of the code.

The people on these boards are mostly other customers and won't know what the missing characters are.

(259623)

Have you tried the link given above ?

You can go talk to customer service.