Not a licensing expert, but here's my take and what I usually do:
The common practice is, if you're selling the software as a service, you are required to have an actual license (professional, enterprise, etc).
This would be the case had a ready to go service and report that would connect to someones database and get the report done, while charging for it.
The best solution is to purchase an MSDN subscription that includes a lot more stuff.
Instead of worrying about purchasing the licenses, I suggest making sure that your bids are high enough to cover all your costs including the licenses, purchasing dedicated systems, etc. SSRS is often an extra expense. You also need to make sure that your bids are high ...
I used to use https://www.toptal.com/tracker/
It has a desktop app that hides in the tray for tracking hours, a web tracker and dashboard, mobile apps, all the things.
It allows you to take screenshots on intervals (or not), generate invoices, and even grant access to your client to view the current hours tracked/logged.
Pretty cool, 100% free and maintained ...