I too had the "purchase failed" problem, until last night when I suddenly had 8 (!) Foundry slots pop up out of nowhere. I went through the character creation just fine until the last step, where I got a "character creation failed" error... and got booted back to my character select screen which claimed I don't have any Foundry slots. Tried again today, and... "purchase failed".
Wuhu, I just noticed I can finally post. My forum account was locked, even though I played on release. Anyway, just can finally say now, that I have this issue too. I had 1/3 characters. Didn't work then, now I have 3/3, but I can delete the 2 new ones again if necessary. I heard the Foundry package is 4 slots? Do I need a 4th character slot? I can buy 2. Then I have 3/5. Or do I need 4 free slots?
When I had 4 characters it didn't work for me. When I deleted one it still didn't work until a day later. I don't know, maybe someone from Cryptis reads this topic and keeps fixing our accounts, but is to shy to notify us about it?