Does the VA just decide to not pay?

So I was on GI Bill till my 26th birthday. I decided to sign up for courses online prior to my birthday to squeeze out the last bit and bolster my college application, however, I came to know yesterday that there I have a $2k overdue balance with the school at which I was attending at the time. Does anyone know what the hell just happened? Why would the VA not pay for courses??

For context, I was on post 9/11 GI-Bill as a dependent, took online courses through CU Boulders MSEE program, and I was considered full time by online standards (at least 3 credits)