The minimum building value (if you are only rating a building and no contents) must be $1,250,001 to qualify for first loss (must be less than 80% - Amount of insurance divided by the actual value).  So if you change the Building Value field to this value and the Building Amount of Insurance to $1,000,000 you should get the quote to rate.  You can then, on the app, overwrite the building value with the actual value.

Note:  This will only apply to CNR risks and not CR risks