Enter the Wix Editor (you need to be on the Editor page, not the Wix ADI).
1.) Press the plus button on the left side to open the "Add" section. This will open a list of possibilities. Choose "More" which is the last possibility on the list. Another list will open with the option "Embeds" on top of it.
2.) Choose "HTML iframe" (see on the picture above). A window will appear on your editor.
3.) Press "Enter Code". A window with "HTML Settings" will open.
4.) Enter the CUSTOM EMBED CODE from the Artist Profile (read here on how to get the code: http://help.optune.me/quick-guide-for-artists/setup/embed-your-gigs-into-your-website-squarespace-wix-wordpress-etc).
5.) Adjust the length, width and position of the integration.
Here is an example of how it will look: https://ashleyafterhour.wixsite.com/website