Paypal pro hosted fails for mobile paypal payments in 2.3.4.1

[tobybailey]

Have just upgraded to 2.3.4.1 mainstream (BS edition next step probably).  Using the paypal payment modules bundled with that (not the possibly different "paypal App").  Have "pro hosted" running but Express turned off.

On the checkout conformation page two Paypal options appear:   a "Pay with paypal" button that I think is implementing Express checkout in some sense and another pay with CC box.

Everything works except that for some mobile devices, if the pay with Paypal option is taken the order is registered and the payment is taken and the sale reported by IPN, but a GET call to checkout_process.php is made by paypal with no parameters.  This leads to the confused shopper being returned to their (still full) Cart.   (In the card payment option a POST call is made and from a Windows desktop a GET call is made with appropriate patrameters which works fine.)    

I have an identical "secret" copy of the shop running on the Paypal sandbox.  There I have turned Paypal Express on.  (I have in mind a long term solution is to turn Express on if it helps but hide the option on the Basket and Checkout payment pages to avoid confusing our not very techy customers with multiple versions of Paypal checkout.)    On the Sandbox version for some reason the Paypal button sometimes demonstrates the same error as above but often fails completely, reporting an "error" from Paypal. 

However, on the Sandbox, if the pay with Express option is selected on Checkout Payment it seems to work completely fine.   So it seems likely the problem is some difference in what happens between the two cases: (a) customer opts for Express on checkout_payment and presses continue and (b) customer opts for Hosted on checkout_payment but then hits the paypal button rather than giving CC details.

I'd be grateful for any ideas! 

Toby

[Jack_mcs]

First, as others will probably tell you, you are using the wrong version of oscommerce. You should switch to the CE version. Once you do, use the installed paypal app. Or, if you don't want to use that version for some reason, install the paypal app. All other paypal modules are no longer supported and will fail one way or another.