I bought an aircraft, but, can't put it on a route

I bought a used 737-8.  I configured it and was able to put it on a couple of routes.  As I continued to add it to existing routes, I started getting the message that I don't have any aircraft to service that route.

I have tried opening new routes, but, the aircraft is never available to add to the route.  It has 135 hours available.

Has anyone seen this before?

Thank you

It's actually a simple answer, Santos.

Either A: it's due to the airport's political restriction, like how New York's LaGuardia and Washington's Reagan National only allow flights along the east coast; Or B: The airport you're wanting to send it to doesn't have a long enough runway.

I hope some of this will help clear things up better.

~Nicholai G.

Do the airport runway is long enough for the plane?

What routes were you trying to operate the aircraft on?