If the other person is the one ghosting, or generally being flaky, it’s not necessarily anything you’re doing wrong. The other person wasn’t in a situation to maintain contact to the degree that you were hoping.

The thing with any friendship, and especially a long one, is that there’s mutual effort in maintaining it, and that you can’t force it, as then it’s a one-sided effort and that isn’t much of a friendship (or relationship more broadly speaking). As Damaskox points to, finding some activity to do together tends to be how many make friends and maintain friendships, so say playing some game or reading books/watching shows at the same pace and discussing them together may be better than if you were only trying to chat.

The trick remains, however, to not make making friends the explicit point of talking to or doing things with others online or offline, as it tends to read poorly even if the intent is to be upfront/honest.