paypal discount amount

no one has came across this problem before, no? and no one has connected their cart to paypal, no?
really?

ok a wee bit more info,

I've written a CMS / shopping cart system with CI 2.1.x (cant quite remember the version I started on) upgraded to 2.2.0 without any problems, using the paypal library by Romaldy Minaya
its a bit old but its nice and simple and has been fine in the past.

I decided to write a discount module for it, quantity discounts, discount vouchers etc,
I've been using the same paypal library for a while, the only problem Im getting is passing the set discount amount to paypal, percentages are working perfectly, a set amount gets ignored, eg a £2.99 discount off the whole cart gets ignored where a 10% discount will pass over perfectly.
I probably could just convert the amount into a percentage `to get round the problem, would be a lot easier if it would just take the variable via discount_amount_cart
My code is fine, even hard coding a value in for testing purposes doesnt do anything, Im getting no errors any where, the value just isnt being used.

No reason for it that I can see (I've written a perfectly working CMS using codeigniter, Im not new to this )

I have seen the same problem on the prestashop forums, but it wasnt relevant to my code, so their fix wasnt any use. Open cart has had the same proble too so it could be a problem at paypals end, some one else must have had this issue using CI, and if not, some one here must be using paypal without problems, no?

A pointer to a paypal library that does work would be great
it would save me time chasing a problem that doesnt seem to exist and give others a pointer to a paypal library that is bug free