Can you please check this article to make sure you are using the attachment function correctly?
If you still need assistance please attach a copy of your process, connection and the service connector.
We will look into this and get back.
I looked at the service connector , connection and the process . Your use case seems somewhat similar to the following KB :
I imported your service connector in my process designer and tested it . Got 401 error.
I suggest you create a support ticket so that we can setup a web meeting and further look into this issue and once you have created the ticket , please post the support case # here and we will reach out to you.