Mo. Rev. Stat. § 408.552: Enforceability of default provisions.

An agreement of the parties to a credit transaction concerning default by the borrower is enforceable only to the extent that:

(1) The borrower fails to make a payment as required by agreement; or

(2) The lender's prospect of payment, performance, or ability to realize upon the collateral is significantly impaired; the burden of establishing significant impairment is on the lender.