$sql = "SELECT Property_number, buildingtype, Address, agent_id FROM property WHERE Property_number = ':propertynumber'";
The single quotes around
':propertynumber'
, means that PHP will treat it as a string literal and not as a parameter keyword. Change the code to:
$sql = "SELECT Property_number, buildingtype, Address, agent_id FROM property WHERE Property_number = :propertynumber";
so the keyword will be recognised as such.