Here:
και δωσω σοι τας κλεις της βασιλειας των ουρανων και ο εαν δησης επι της γης εσται δεδεμενον εν τοις ουρανοις και ο εαν λυσης επι της γης εσται λελυμενον εν τοις ουρανοις (Matthew 16:19)Which is
And I will give to thee the keys of the kingdom of heaven. And whatsoever thou shalt bind upon earth, it shall be bound also in heaven: and whatsoever thou shalt loose upon earth, it shall be loosed also in heaven.
αμην λεγω υμιν οσα εαν δησητε επι της γης εσται δεδεμενα εν τω ουρανω και οσα εαν λυσητε επι της γης εσται λελυμενα εν τω ουρανω (Matthew 18:18)
Which is
Amen I say to you, whatsoever you shall bind upon earth, shall be bound also in heaven; and whatsoever you shall loose upon earth, shall be loosed also in heaven.
So where is your "error" and "The Greek word is eimi"?
δεδεμένα and λελυμένα (bound and loosed) are both perfect participles middle/passive.
The significance of the perfect tense means an action was completed in the past but with results existing in the present time(in relation to the speaker/writer).
These are more properly translated as "shall have been bound" and "shall have been loosed".
δήσητε and λύσητε (you shall bind and you shall loose) are both aorist subjunctive active verbs. These are both proceeded by ἐὰν (if) which makes this part of Matthew 18:18 a third class conditional statement. Third class conditional sentences always have a protasis introduced by ἐὰν and a verb in the subjunctive.
These are more likely classified as future more probable third class conditional sentences. If the first part of the if statement is true, the then part of the statement is also probably true.
To interpret this....Jesus is saying whatever you may bind or loose on earth has already been bound or loosed in Heaven. The disciples were to make their decisions in these matters on what was already known.
NASB, HCSB, NET Bible, Aramaic Bible, KJ 2000 Bible, World English Bible, and Young's Literal Translation all have Matthew 18:18 along these lines.
Please ping me if you ever get an answer from the bear.
και δωσω σοι τας κλεις της βασιλειας των ουρανων και ο εαν δησης επι της γης εσται δεδεμενον εν τοις ουρανοις και ο εαν λυσης επι της γης εσται λελυμενον εν τοις ουρανοις (Matthew 16:19)
αμην λεγω υμιν οσα εαν δησητε επι της γης εσται δεδεμενα εν τω ουρανω και οσα εαν λυσητε επι της γης εσται λελυμενα εν τω ουρανω (Matthew 18:18)
There, I highlighted them for you.