I have two issues with Marketpress 3.
1) The checkout page is blank.
2) The affiliates integration is missing.
As for the checkout page...
I have experienced the issue on a live site and have spent days troubleshooting it. While I have not yet been able to fix it, to me it appears to be a database issue.
1) Restored the live sit to a test site (verified it still didn’t work)
2) Disabled all plugins (no luck)
3) Switched to 2015 default theme (no luck)
4) Uninstalled and re-installed the Marketpress Plugin (on luck)
3) Did my usual base install (which is more than just standard Wordpress but does not include the Marketpress plugin) - then, installed the Marketpress plugin, created a product, did a test buy and was prompted for the billing/shipping info (worked).
4) Restored the 'non-working' install to a test server and overwrote the database with the info from the same file used in step 3 - enabled the Marketpress Plugin (worked)
On the non-working copy, when I enabled debugging, the page was still blank. No errors were reported.
If I go straight to the page with the [mp_checkout] shortcode on it and have nothing in my cart, I get "Oops! Looks like you haven't added anything your cart. Let's go shopping!" So the shortcode is working and, apparently, returning a completely empty result set.
If you can send me info on how to trap what's going on when the [mp_checkout] shortcode runs, I can look at it and (hopefully) help resolve this.
Note: The issues remains unresolved on 220.127.116.11
Note2: If I downgrade to the last 2.9 lite version, the checkout page appears.
As for the affiliate issues...
I have the appropriate add-on installed but can't see anywhere in the products or store to setup affiliate sales/commissions.