How to correct if no permissible payment event?

There is an agreement subject to 409A that provides that a bonus is earned upon a sale of the company. However, it does not provide when or how that bonus is to be paid, is there anyway to correct under 409A? There is going to be a sale of the company, but the plan provisions don't state when payment is to be made (i.e. lump sum, installments...)

How do you know the agreement is subject to 409A?  are there other payments within the agreement subject to 409A?  What does the agreement state with regard to payment?  It is hard to answer 409A questions without more context and language.  Note that there are arguments that you can correct a 409A failure prior to the year of the substantial risk of forfeiture lapses or even in the year the substantial risk of forfeiture lapses but prior to the date the substantial risk of forfeiture lapses.  See Chief Counsel Advice Memorandum 201518013; 1.409A-4 (can't remember if in proposed regs or final).  If this is the only payment under the agreement, it seems that arguably the sale should be considered the "vesting" event and the document failure may be able to be corrected if the sale hasn't occurred.