Presumably the new money is in exchange for some newly-created class of preferred shares. Stripe holds the cash until it repurchases common shares from employee

Presumably the new money is in exchange for some newly-created class of preferred shares. Stripe holds the cash until it repurchases common shares from employees or any other holders, and those shares would go back into the unallocated common stock pool I'd assume. So yes, I'd think the only way this works is for Stripe to be the purchaser.