If the order is canceled, it means that in the "invalid status" option of the PayPal plugin you set "canceled" and that the notifications sent by PayPal cannot be validated. You should have received an email as the administrator which explains what is the problem with a link to the documentation for the problem. Isn't that the case ?
What does it say ?
If not, you should turn on the debug mode of the PayPal plugin, try again, and then look at the payment log report in the Files tab of the configuration of HikaShop. That should give some information about the payment notifications sent by PayPal.