if only states can make agreements, then the palestinians will never be able to have a state since they are not sovereign. international law specifically recognises that under certain circumstances, non-state actors can enter into international agreements. such has been the case with the pa as a result of the oslo agreements. resolution 242 is the roadmap for such an agreement.
Woman moderately wounded by firebomb thrown at her car in north J'lem (Haaretz)
from the article: Abbas must unilaterally declare Palestinian state