Where to store financial transactions of the payment system?

Question

Information Security

Good afternoon! I design a payment system for internal payments between the company's clients.
Goal: To provide 10,000 clients of the company with the possibility of mutual settlements and transfers of funds between their accounts with a transaction speed of no more than 5 seconds in 80% of cases and a maximum amount equivalent to 30,000 euros per day per client.
Reliability requirement: The system must be able to tolerate no more than 1 failure per 10,000 transactions with a maximum recovery time of 30 minutes.
I have different kinds of data:
Logins and password hashes. Key risk: Loss of system owner access cannot be allowed
Customer data, personal data and reference data. Main risk: Data leakage.
Scanned copies of documents. Main risk: Slow data writing and retrieval (large volume). Data leak.
financial transactions. Main peep: Data changes cannot be allowed. At the same time, it is necessary to ensure an acceptable transaction speed. Data cannot be lost under any circumstances.
Event log (user authorization, user actions). Main peep: Data changes cannot be allowed. The write speed must be high.
Application settings
Log files
Generalized management data (OLAP cubes, data marts)
The most painful issue in financial transactions. Where is the best place to store them? Blockchain?
And most importantly - how can we justify the fairness of the choice of this or that decision on the basis of numbers?

Answer 1

Where is the best place to store them? Blockchain?

Oh, this fashion.
Blockchain is counterfeit protection.
Provided that someone will independently maintain a duplicate of transactions.
Thus, you will not be able to deceive this someone.
Will you have such someone (is it an independent organization / independent person)?
If not, then no blockchain, there will be no benefit from it.
Otherwise - a normal DBMS server with synchronous replication, but at least PostgreSQL.
And ordinary signatures, even with the RSA algorithm

Answer 2

Good question, long and detailed. It is immediately clear that you figured out what you need.
Here, this is a centralized system, such existed 500 years before the invention of the blockchain, since the advent of banks (I gave you a figure to justify it).
Now go and shake the garbage out of your head. Maybe it will help.

Answer 3

Give the keyboard to adults. It's not yours...