Have you completed the "Account linking required" in the skill? .. it is not enough simply to enable the skill.
-- from the bring website it says:
How do I connect Bring! to my Amazon Echo? First, download the Bring! skill from the Amazon Store. You can then connect the skill to your Bring! account in the Alexa app. You will have to set a default list in the Bring! skill to which all items will be added when using the Bring! Skill. Please also note that you always have to start the Bring! skill each time before adding items to your list.
Go to your Alexa app -> skills -> Bring Skill -> and complete the "Account linking required".