We have 28k miles expiring at the end of August.

What is the easiest most cost effective way to extend them? We wont have time to have anything credit to the account prior to 31 August (we dont have a marriott account active to enable them to be transferred)

Is it as simple as sending 100 points to the Fly Greener cause? We have tried this but kept getting the same error saying session had expired/need to log in.