Hi Paul.
There may well be a neater solution than this, but i have got it to work, (still using ecart4)
(i will link to this thread in case a better solution comes along)
Assuming you have a session variable being triggered correctly...
in the discounts tab, create a discount rule called £25 off £500+ or something
in the triggers,
Conditions should be session varaible SESSIONNAME == code
AND SubTotal of items >=500
AND SubTotal of items <1000
Flat rate discount of £25
create a second discount rule called £50 off £1000+ or something
in the triggers,
Conditions should be session varaible SESSIONNAME == code
AND SubTotal of items >=1000
AND SubTotal of items <1500
Flat rate discount of £50
etc.
if the threshold of £1000 is reached, the first trigger will not fire, so discounts are not duplicated.
The thing I don't like about this approach is, if you get a huge order, you have to put sufficient rules in to account for this
hope this helps