Is this a return you originally prepared/efiled ?   Have you marked all the check boxes on the Federal Information Worksheet for Filing Amended Return

Here is ProSeries instructions  https://proconnect.intuit.com/support/en-us/help-article/amend-tax-return/amending-individual-return...

I agree. Make sure you followed PS amended return instructions correctly. If you can't make it efile, print it, have client sign/date and send by Certified mail (so they know when it was accepted)

I had the same problem in ProSeries Professional with an amended 2021 return that I did not originally file.  I was able to successfully file another amended return, same year previously.  This file had the same Error Code IND-463.   2 1/2 hours on the phone with tech support and no resolution.  I called back and got another rep who said IND-463 is an IRS code and I should call the IRS.  Unfortunately the IRS Eservices help desk was closed for the day (and it's Friday).  Will call on Monday and let you know what the IRS says.

I am also going to start another file from scratch and try the process again in case the multiple Error messages from Intuit are preventing this file from being successfully transmitted.  Either way, I'll let you know how it is resolved.  

Try changing your PIN DATE to 12/30/21

When I change the PIN date to 12/30/21, I get a diagnostic error message that the date must be from 2023.  Won't allow me to Efile.  Is there a way to turn off the diagnostics?  I'm new to Proseries. Your suggestion is more help than I have received from tech support regarding this issue.  I really appreciate the input.  

I changed the PIN Date to 12/30/21 and disabled the error diagnostics, but the 1040X box on the Efile window is still greyed out and can't be selected.  The error code indicates the 1040X is missing from the return, even though all of the appropriate boxes (Efile 1040, Efile Amendment, Check to see if 1040 is filed) are checked.  

This appears to **bleep** in Proseries.  I'm going to try to file this with my other tax software.  I never had this problem with other vendors.

Uncheck file federal tax and make sure your Amended returns are marked in Part VI. Also Fed return filed successfully .Then go to Efile at top of ProSeries and Marked Amended returns ready for Efile in both Stateside and Federal.

Were you able to finally file the 2021 amended electronically?  What did you do?

This is SO ridiculous.  I keep getting conflicting errors.  If I don't check Part VI (federal electronic filing box), Proseries gives me an error stating "Cannot electronically file Form 1040X when the original return is NOT marked for eflle Part VI", so I check it - then it gets rejected stating "If Federal return is not being filed, UNCHECK Federal Electronic Filing box in Part VI".  From what I am reading, proseries help is useless (what a surprise) and it seems as though the only resolution is to mail it in.  Kind of defeats the purpose of proseries

I've never been able to efile an amended return if the original return was prepared somewhere else. Proseries software just fails. If I follow the instructions, I get errors. If I don't follow the instructions, I get errors. This is not only unacceptable nowdays, it borders on creating fines and penalties.