Hi Tim,
I have found the source of the problem.
if($price_check != @$vars['mc_gross'] || $currency->currency_code != @$vars['mc_currency']){
If you read the log details of your last order (U18), you would see that the HikaShop order price is 0.50 £ and there is not taxes.
In the paypal return, the price is different.
Array
(
[mc_gross] => 0.60
[tax] => 0.10
[mc_shipping] => 0.00
[mc_handling] => 0.00
[mc_fee] => 0.22
[mc_gross_1] => 0.50
[mc_currency] => GBP
)
As you can see, Paypal is saying that the full price is 0.60 £
So HikaShop can't validate an order if the price you paid is different than the order price (Otherwise you could paid less).
That is the source of the error.
Regards,