Depending on where the lump sum was coming from, you would need to offer as close to or more than the promised dividend.
If for instance, the money was from such as a lottery win which would enable you to pay back your original debts then that would be what you needed to pay.
You should ask your supervisor to work out a figure for you based upon returning the original dividend as a starting point. Where would you be able to get funding from to make this offer?