The best option to use vMix with Loola is via Loola's RTMP Mode and vMix "Stream" option.
First, select RTMP mode in Loola to find you RTMP Key and URL:
Open the stream settings in vMix:
Copy and paste the RTMP URL and Key from the Loola Studio to vMix:
Configure the Quality/Encoder settings:
See recommended platform encoder settings here:
Click the Stream button in vMix to start the preview in Loola:
Once you can see the vMix video preview in Loola, you can select your destinations in Loola and click Go Live: