Mo. Rev. Stat. § 429.210

The court shall ascertain, by a fair trial in the usual way, the amount of the indebtedness for which the lien is prosecuted, and may render judgment therefor in any sum not exceeding the amount claimed in the demand filed with the lien, together with interest and costs, although the creditor may have unintentionally failed to enter in his account filed the full amount of credits to which the debtor may be entitled.