I'll try to outline this quickly.
Two equal, 50/50, partners - one is building/creating the product, running all operations, etc…the other is footing the bills and will be doing the sales.
At the beginning the partners agreed that the partner creating the product would garner the first $100K of product sales before the second partner drew a salary. This is because the first partner, the builder of the product, worked on this full-time - usually 80 hours a week, for a year, while the second partner invested about $10K per year.
Now, that's not to say if we received orders for $25K per month, for a year, we'd obviously just split it at that point. But, if orders came in, for the first years at a rate of $5-10K per month, this money would go to the first partner as payback for his 4000 hours of product development.
Now the second partner - who at this point, now that the product is ready to deliver and reviews are excellent, is little more than an investor - is demanding that everything be split 50/50 from the very first check we get. Which goes against his written agreement.