Nguyen Ngoc Nhu Quynh was 16 months into a 10-year anti-state propaganda sentence.
Police objected to slogan on T-shirts being sold, while officials said the concert had been held without permission.
Lack of funds forces security ministry to generate alternative sources of income.
They agree to the establishment of a single army and to extend dialogue to groups outside a key 2015 ceasefire accord.
