marketpress checkout from multiple stores using chained payments?

Is it possible to set my website up so that a customer can purchase from multiple stores in one checkout process using marketpress and chained payments?

Currently I can add a product from one store and successfully checkout using the paypal chained gateway - which is a great start. But I want customers to be able to purchase site wide.

I have tried testing this and can't get it to work.

I add a test product from one store and all is fine, add from another store and the first product disappears from the cart - I can checkout the second stores product but the first has disappeared.

I tried following this advice https://premium.wpmudev.org/forums/topic/marketpress-global-cart-plus-chained-payment and resetting global cart on network admin. This allows me to add multiple items to cart successfully but stops working at the point of payment and gives me a paypal error.

I need this to work, I would really appreciate any help.

Thank you

Nicola