I follow the posts on this forum because Sliced Invoices is integral to my business operations and my clients love it and I just have to say reviews like this irritate me. First off, I have had one issue that I put a ticket in for and got excellent support for it from Andrew. He told me turn on debug mode and it turned out A DIFFERENT PLUGIN is buggy and was interfering with WordPress being able to send emails out properly, so maybe that’s your problem.
Or maybe your problem is something else. But if you don’t put in a support ticket, you can’t expect to get help.
Also I installed and demoed just about every other invoice plugin for WordPress, and though it may not be perfect, but it’s the best one available. So for sure, “look further,” maybe invoice outside of WP. But you’ll probably be back.
Thanks for a great plugin, David!