Funny enough, (and I don't speak for ASC, im merely a member in their community discord)
they had set up their paypal account to take orders, and the influx of money/orders on august 1st got them flagged and shut down by paypal.
after fighting their case with PP support, they couldn't get it opened again.
IDK if or when they'll offer paypal after that negative experience.. LOL!
Due to recent steam policies- You cannot put a pre-order on DLC unless a release date is given.
now, with the Mig29 ED actually put the release date as the very last day of september- and those with a keen eye would notice, that before the pre-order opened on steam, it was marked as either "TBD" or coming soon. But as soon as pre-orders open there has to be a release date.
What I have seen 3rd parties do- is to have the product release on steam on launch day- and keep the pre-order discount applied on the steam store for a week or two, HB did it with the Phantom since they avoided opening pre-orders on steam, so they offered the equivalent discount amount for a few weeks post- release.
GUCCI's post in Yo. Attn: ASC: Payment options was marked as the answer