Yes, WileyWon, my eventual experience was exactly like yours. After experimenting with TurboTax and not making the numbers "add up" I read the Virginia Dept Taxation's instructions, which in retrospect, I should have reviewed initially. So as the VA Dept Taxations says, my amended VA 760 form does NOT include the amount I paid in April. Instead, I placed this figure into line 1 of the "worksheet for amended returns". TurboTax indicated the correct (I hope!) amount owed on the worksheet and the summary page. When I tried to submit the taxes electronically, I received the same error message you did (Tax Year 2023 transmissions are not available...). I ended up printing and mailing a hard copy of the amended VA return. And just as you mention, sending the Federal amended return electronically worked fine.
Seems like TurboTax program is missing a section on the Virginia Worksheet for Amended Returns data.
An additional issue was that the number that TurboTax automatically placed into line 1 of the "worksheet for amended returns" seemed to be a random number unrelated to my tax data. I have no idea where that was coming from and manually corrected it.
