Just set it to conditional moves.
The website is obviously reluctant to just give people victories if they have a forced checkmate. Firstly its unfair on an opponent who loses if they want someone to play for checkmate. Secondly you might not know how to get checkmate anyway (although not saying this is the case in your particular game you are on about.)
Let me state for the record this was a completed game in an on-going (ruy-lopez) tournament. It occurred to me there is something with the system concerning on-line chess on this site. If i announce to my opponent a forced mate in 8 moves or less at (7 days per move) why should i have to wait until christmas to claim the victory should my opponent decide not to resign ! ( he resigned) . Where is the verify tab to justify my claim and end that contest or not justify my claim costing me an automatic forfiet either way at least i will be home for Christmas !!