Real Estate Law
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Under Florida law, if the service is not made because of the fault of the USPS, you cannot be held liable. You can proceed with the action. I would suggest that you just send it again, and once you send it, if the other party tries to fight it, then your defense is that you attempted service and it was the error of the USPS. Under these circumstances you will prevail.
Good luck to you. Please rate 4 or 5 and close out the question. I wish you all the best.