Is it permissible to accept financial compensation after a purchase request from a website is canceled, even though the item is still available at a higher price, and it was possible to purchase it at a similar price from another website at the time of purchase?

If the website offers compensation willingly and by its own choice, and is not forced to do so, then there is no harm for you in accepting it, especially if the compensation does not exceed the amount of the price increase of the commodity, so that it is equal to the amount of actual damage.