tl;dr If you're from SEA and have a problem when trying to purchase in game currency try to buy 5150 AC, 10300 AC, and DLCs that are not listed as in game currency(ex. sonic collab) instead. We reported the problem to pso2, they said they'll look into it, but they didn't give an exact time about when the problem is fixed.
I got a response from them and this is what they're saying, I also told them to check the SEA region not just Indonesia since there's someone from Vietnam that has this problem too.
"Greetings ARKS Operative!
Thank you for that information. We will continue our investigation, however due to the complexity of the issue, we do not have an estimated completion date. We will contact you when we have an update.
Please also keep checking our website and various social media for any new details about this issue.
Gratitude for your support.
- Your PSO2 Team"
So everyone from SEA probably not gonna be able to buy AC anytime "soon" since they don't give the estimated completion, well I hope at least this problem will be fixed.