If you can't send or receive direct messages in the AGCV Community, it's almost always one of two things: a setting on your own account, or a block from a specific member.
Check your own messaging setting
Go to Profile → Privacy (or Edit profile on mobile) and check whether Prevent members from messaging me is turned on. If it is, turn it off and save - that alone resolves most DM issues. AGCV admins can still reach you by DM even while this setting is on, but you won't be able to message or be messaged by other members.
If that toggle appears greyed out and you can't change it, contact info@agcv.com - this usually means an account-level restriction that needs staff to adjust.
Check whether a specific member has blocked you
If one particular member has blocked your direct messages, you'll see a "This member is not receiving messages" banner in your existing conversation with them (or "Messaging disabled" on mobile). The block only affects that one relationship - you can still message everyone else. To reach that person again, they'd need to unblock you first.