Allow to Purchase multiple subscription at once

There's a setting in the module to enable support for multiple subscriptions. It's named "Multiple plan mode" and the description says "Single-plan mode allows users only one subscription at a time, preventing them from having multiple plans active simultaneously. Use Multiple-plan mode if each user is allowed to sign up for more than one subscription at the same time."

I've never personally used the module in multiple plan mode so I can't speak to how well it is supported. But I think testing that out, and seeing if it gets you what you need. And reporting any issues here. Would be a good place to start.