For one of our client, still using Spree 0.70.x (the update to Spree 1.X is planned soon), we needed a working version of the official Spree Paypal Express Gem.

Turns out that you need a specific commit to run, plus the extension wasn’t setting the flash[:commerce_tracking] properly, so I’ve bundled all this into a fork that you can find on my Github page.

I hope it might be useful to someone else one day.