Johannesburg - Eskom is investigating the cause of slow performance on its prepaid online vending system, the electricity parastatal said on Wednesday.
The system is used by prepaid customers to purchase electricity tokens.
Eskom added that while the system was not down, its performance was slow.
"Customers can still purchase their prepaid tokens but the process may take longer than normal," it said.
Eskom also had technical issues on its vending system last year.
"Remedial work has been done and the system is more stable but we are still working to improve the performance of the system."