Modern Format - A deck's sideboard must have exactly 15 cards.

{"ops":[{"insert":"I have this deck "},{"attributes":{"link":"https://archidekt.com/decks/110513#Mono-Red_Prowess"},"insert":"https://archidekt.com/decks/110513#Mono-Red_Prowess"},{"insert":"\n\nThere are 15 in sideboard, but there is still a message stating a sideboard must have 15 cards. I tried removing and adding multiple cards, but the same message appears.\n"}]}