So I'm one of those unfortunate people who has been running Modernbill since v4 and I am actually still running PleskBilling v6.0.3, until today (almost). I have run into an issue (big surprise) where it seems to think my clients haven't paid their invoices and so it isn't running domain renewals. Those customers have a $0.00 balance. Trying to even find a way to get support from Plesk was a joke. They bought Modernbill, and now, unless you have the Plesk and Pleskbilling bundle, you're screwed. The standalone code is sitting on a shelf gathering dust somewhere and I'd be surprised if they even staff someone to support it.
With all that said, and finding this post confirming my desire to move away from PleskBilling, I'm wondering if there's an import script for v6.0.3. The main site here says it has import scripts for v4 and v5, but I didn't see a mention of PleskBilling v6. This is the only thing stopping me from ordering a license for WHMCS right now, so if someone can confirm that I'll be able to import everything without having to do it by hand, please let me know!
Oh, I forgot to mention that every time I login to PPB it tells me my license key has expired and I have to reactivate it. I have an owned license... why would it expire?