I have a problem i would like to adress. I dont use cron or plugin for automated invoicesending.
When i select multiple customers for manual invoice sending and hit the email button, it takes a long time before anyting happens, get a server error (http 500 server error) and cant acces the joomla back end for a wile. When I acces VM invoice again, I only send a couple of incoices.

How can I address this problem?

Hello,

well, the problem is, that the invoice generation takes some time. So when generating multiple ones, it may end up on server timeout. You need to send them in smaller chunks in such case. E.g. 5 at time; or you need to modify the server setting to allow longer script run.

I am afraid there is currently no more effective solution.

We plan some new features that should "precache" the invoices, so then just sending them will be faster, but this feature is not available yet.