Update. Our site just received another duplicated order. The reason is, the interval between the duplicated submission is over 60s. Not sure why but our site tried to submit a total of 6 times for this order.

I will update my interval in my code from 60s to 150s (2.5 mins) and see if it helps.

Also, I'm not sure if it is normal that paypal will take about 3s to process each payment submission?

Timestamp by the paypaldp log files:

2023-03-18 10:18:03 success INVNUM 27985818
DoDirectPayment, Elapsed: 3047ms -- Success

2023-03-18 10:18:04 Failure INVNUM 27985818 Paypal auto denied
DoDirectPayment, Elapsed: 2508ms -- Failure

2023-03-18 10:18:04 Failure INVNUM 27985818 Paypal auto denied
DoDirectPayment, Elapsed: 2509ms -- Failure

2023-03-18 10:19:11 success INVNUM 27985819
DoDirectPayment, Elapsed: 3119ms -- Success

2023-03-18 10:19:12 Failure INVNUM 27985819 Paypal auto denied
DoDirectPayment, Elapsed: 2926ms -- Failure

2023-03-18 10:19:12 Failure INVNUM 27985819 Paypal auto denied
DoDirectPayment, Elapsed: 3107ms -- Failure