integration with Slack

i upgraded my Box account to integrate with Slack. 

my company is looking for the following: 

Through Slack, all attachments from all users in our workspace to go straight to our Box account. and documents for signature to be also attached through Slack, but saved and signed through Box. 

what happened is that only the attachments from my user are being saved in Box and no one elses. 

also, i couldn't figure out how to get the documents to be signed by Box when they are attached in Slack. 

Can you help me with this issue please. this is of high importance to improve our work processes.