Why can't I claim or delete mail rewards with storage space?

I have 2K on each of these in my depot and I got none in my backpack. Why can't I claim it? The orange dot is killing me. Edit: It goes to the Backpack... man like seriously? Can't they just separate these? 2 mails 600 each? And specify that these will be sent to "BACKPACK" slots. Man. "Storage Slots used Up, Destroy or Discard some items and try again". Since my Backpack has 2 Rows filled and 5 rows unfilled I wouldn't first assume that it was my Backpack since I have a space. I'd assume they would still be put in the backpack but decrease the attachments left but instead they just don't. Dumb stupid implementation.