Authorize.Net error. E00027: A duplicate transaction has been submitted.

[Ghopper21]

After no problem for many years, I started intermittently getting the following exception when submitting a payment transaction: Authorize.Net error. E00027: A duplicate transaction has been submitted. There is no obvious cause, i.e. no duplicate transaction from my end.

I spoke with Authorize.net tech support and said they are seeing a duplicate transaction coming through a few seconds apart, and suggested that sometimes the API framework does this for technical reasons.

It's a mystery to me because nothing has changed in my Django app. The error started a few days ago and since then has been varying between happening more than half the time to happening less than 10% of the time.