I am using Magento and am trying to apply a coupon code which discounts a fixed amount of £5 off any order over the value of £149. The code is working fine until two different items are added to the cart. Even if the value is over £149, as soon as there are two or more different items the code is discounting seemingly random amounts such as £2.33 or £1.21. The amount seems to vary with the number of items in the cart as soon as a second item is added.
The code is configured as 'Fixed amount discount for whole cart' and did work previously, I'm not sure why this glitch is occurring now. Is anyone able to advise please? Thanks in advance.