Bottom line: you have real stick options that don’t require his voluntary sign-off:
• Trigger the Capitalization Default and Buy-Out Right.
• Structure a partial sale to invoke the 20% haircut.
• File for equitable dissolution/receiver or injunctive relief.
• Record a lien to force an Involuntary Transfer buy-out.
• Use mortgage guarantee mechanics to squeeze him financially.
Your next step is to pick the lever(s) you’re comfortable pulling and signal he must either fund or face a lawsuit that will cost him far more in time, fees and dilution than simply putting in the money he agreed to. Let me know which path you want to take first—and I’ll sketch out the exact notice or complaint you need.