Of course, get a lawyer. That said, > I made a mistake in that I agreed to the 20% royalty rate without negotiation initially, I know that much This is the r

Of course, get a lawyer. That said, > I made a mistake in that I agreed to the 20% royalty rate without negotiation initially, I know that much This is the root of the problem. You were always hoping some day this would be corrected, and now that day is here. I'd recommend crunching the numbers and back this up with data. There should be spreadsheets and charts made of sales figures, expenses, salaries, profits, loses, etc. Prove to your partner that you didn't really get a fair deal as the deal doesn't consider a sale. You should get more simply due to the change in risk.