If it's Foundry Slots your trying to purchase I had the exact same problem it always said "Transaction Failed"
The following method worked for me:
(I assume you have an empty character slot anyway as you'll need it for a test character)
1. Create New Normal Character on Holodeck Server
2. Once created and in game log out
3. Delete Newly created Character (Freeing up that slot again for Test Character)
4. Immediately move to Foundry and Purchase slots (You should see 2 and 4 available - I bought 2)
5. Create Foundry Test char (Use Default settings this is bugged as well)
Anyway this worked for me can't guarantee it'll work as I only have one account to test on but you lose nothing trying.
Well, I've tried that workaround method and it does work to create content. However, if you exit and go back in, it will tell you that you X/0 slots available and you can't go edit your projects. The only around this is that workaround method again.