The phrase "agreement on the matter" means that people have reached a mutual understanding or have the same opinion about a particular issue or topic. Full definition
The couple is not asked to award custody, alimony, child support or property to either party because the parties have already reached agreements on these matters. (nj-mediator.org)
The surveyed men and women were in agreement on this matter. (datingadvice.com)
That having been said, it seems that we find ourselves in reluctant agreement on this matter. (religion.blogs.cnn.com)