Instead of just saying you're missing the items, it should tell you which items are missing.

I like how this is shown on the Achievements page for achievements that require items. That is, the items are shown in red, but items you have are shown in green with a checkbox underneath. I'd really like to see something similar for quests, because it's a pain to then have to go to my inventory to figure out what I'm missing.

I'm not too opposed to this suggestion but... while achievements can require dozens of items, quest is mostly just two. Searching inventory isn't necessary either, I go back to quest page and account search items from item hover.

I'm like here it's not awful but its not really necessary either.

If you sort your Inventory by Timeline before you start Quests, then your most recent purchases are at the bottom of all your items press Page Down. You don't need to do any searching at all.

I like this idea, quests are time sensitive and anything that speeds things up is helpful. If you're missing something you thought you already bought, then you have to check your inventory, re-buy the item and then get back to the quester from the error message.

If the questers instead makes items green/red or checked, you don't even need the error page anymore, you can immediately tell you're missing an item, which item, go buy it and submit again.

I think it's a nice idea! sometimes I am space cadet