I’m having some trouble conceptualizing the notion where there’s a secondary market buyer of private company who’s obliged to transact at a given price, but mig

I’m having some trouble conceptualizing the notion where there’s a secondary market buyer of private company who’s obliged to transact at a given price, but might go higher. Is the idea that a secondary market buyer struck a deal with Carta’s capital markets division that if Carta can locate shares of XYZ startup, then the buyer agrees to buy those shares at $x, but may pay the investor more if (for example) a higher price is a condition of the board’s approval of the transfer?