KJV: 25 And when ye stand praying, forgive, if ye have ought against any: that your Father also which is in heaven may forgive you your trespasses. 26 But if ye do not forgive, neither will your Father which is in heaven forgive your trespasses.”
NIV: 25 And when you stand praying, if you hold anything against anyone, forgive them, so that your Father in heaven may forgive you your sins.” 
ESV: 25 And whenever you stand praying, forgive, if you have anything against anyone, so that your Father also who is in heaven may forgive you your trespasses.”
CSB: 25 And whenever you stand praying, if you have anything against anyone, forgive him, so that your Father in heaven will also forgive you your wrongdoing.”
Mark 11:26 is added from the parallel passage in Matthew 6:15.
Matthew 6:14 For if you forgive other people when they sin against you, your heavenly Father will also forgive you. 15 But if you do not forgive others their sins, your Father will not forgive your sins.
Nothing is lost as the verse occurs in the Matthean parallel.