Dropbox Integration: Submission PDF is not sending to Dropbox

I've just set up a form and wanted to store form submissions in a Dropbox folder. However none of my test submissions has resulted in anything appearing in the Dropbox. I've removed and remade the integration a couple of times but with no joy.  I'm sure I'm missing something (I've set up Dropbox integration on other forms before now but it was a long time ago!) but can't see what! Can you assist please?

Thanks for reaching us.
I have checked your form. Integration was built correctly. 
Your submission PDF and uploaded files must be sent to Dropbox. There will a bug on our side. I am reporting this issue to our back-end team.
You will be informed here.

Hello @ShiplakeVillages!
I have submitted your NP Supplementary Survey March 19 form once. Can you please check your DropBox for my submission PDF is there or not?

Hi Alan,

Your response caught me by surprise as your action resulted in the problem being resolved promptly back in March. Coincidentally I'm just about to launch a follow up survey and I'm pleased to report that the integration for that seems to be working fine. Thanks for your help,

Gareth