What Are the Risks of AES-GCM [Key, Nonce, Message] where Nonce = Message
I think this is a bad idea for a few reasons:


In GCM mode, if you encrypt two messages with the same nonce, then the messages' plaintexts may be retrievable from the ciphertexts. So if you have two different messages about the same customer that both use the customer id as the nonce, then your encryption may be broken.
When a user retrieves a ciphertext, how will they know the customer ID to use as the nonce? Usually the nonce is included with the ciphertext so that the user can use it with the key to decrypt the ciphertext, but if you do this, then the customer ID will be in plaintext.


Is there some reason that you don't want to use a random nonce as is normally done? If there isn't a specific reason to go off the standard path, then you should avoid doing so.