Maybe this has been said before.
Optimizely does not allow for referral exclusions. This means having an external payment provider completely destroys any channel data within the Optimizely interface. I argue that this makes transaction analyses on a source/medium level virtually impossible for a large part of the e-commerce parties.
The only way to reliably measure your channels in tests is via GA. Which should not be the default.
Optimizely and GA cookie gather data in the same way, but treat it differently
user 1: - session 1: [google / cpc]
- session 2: [direct / none] - [buckaroo.com / referral] // Buckaroo is a payment provider.
user 2: - session 1: [google / organic]
- session 2; [affiliate1 / refferal] - [buckaroo / referral]
Both GA and Optimizely would measure 3 sessions per user based on the normal cookie configuration. For user 1 this would be cpc, direct and referral. For user 2; organic, affiliate and referral. This last referral is not a separate session, but a payment provider needed for transactions on the website.
In GA we can add Buckaroo to the referral exclusions, so it does not overwrite the original source medium. However, we wish to execute more simple tests within the Optimizely interface in stead of GA. Here a transaction is always attributed to referral, thus losing all channel data for transactions.