Financial module of the exchange

Technical task: financial module of the exchange with system commission

1. User accounts

• An internal balance is created for each user.

• Account currency: EUR.

• Balance changes only through transactions.

• Account statuses: active / blocked.

2. Automatic account replenishment

• Integration with the payment system stripe via API.

• After payment confirmation:

  • funds are credited to the user's balance;

  • a transaction of type deposit is created.

• Processing webhooks.

• Protection against duplicate payments.

3. Automatic withdrawal of funds

• The user submits a withdrawal request.

• The minimum amount is a system parameter.

• Statuses:

  • pending

  • approved

  • rejected

  • paid

• At the time of the request, the amount is blocked.

• Complete log of status changes.

4. Reservation and payment for domains / websites (with commission)

• When reserving a lot:

  • the buyer's funds change to reserved status;

  • the reservation lasts for N minutes (configurable).

• After agreement confirmation:

  • the full amount is deducted from the buyer's account;

  • the system commission is automatically withheld from the seller;

  • the seller is credited the amount minus the commission;

  • the commission is credited to the system account of the platform.

• If the agreement is canceled:

  • the reservation is automatically returned to the buyer.

• All actions are recorded as transactions.

5. System commission

• The commission is withheld only from the seller.

• Types of commission:

  • percentage of the transaction amount (for example, 5%);

  • fixed amount (optional).

• Settings:

  • global commission in the admin panel;

  • ability to change without code rework.

• Commission:

  • is displayed to the seller before agreement confirmation;

  • is stored separately in transactions (system_fee).

• It is prohibited to complete the transaction if:

  • the seller has an incorrect balance;

  • there was an error in calculating the commission.

6. Account history (user)

• Types of operations:

  • deposit

  • withdrawal

  • reserve

  • release

  • sale_income

  • system_fee

• For each operation:

  • date/time

  • type

  • amount

  • status

  • related lot

• Filtering by period and type.

7. Statistics for the administrator

• Total system balance.

• Separately:

  • user funds;

  • reserved funds;

  • funds for withdrawal;

  • platform income (commissions).

• Analytics:

  • commissions for the period;

  • top sellers;

  • exchange turnover.

• View any user's account.

• Export data to CSV.

8. Technical requirements

• Backend: Java Spring Boot.

• ACID transactions.

• All amounts — BigDecimal.

• Audit log of all financial operations.

• Protection against race conditions.

• Tests for:

  • deduction;

  • reservation;

  • commission;

  • rollback on errors.