I have tested SendMail, PHPMail and SMTP on my end and all work fine on my end(although possibly due to the changes discussed below. You can find the last version of FusionInvoice on Github.
https://community2.invoiceplane.com/t/topic/6356/8?u=cincinnatimattie
I’m sure there will be a fix for this in the next release but until then you can work around the issue. Sorry, I don’t know enough to offer a more permanent solution.
The account isn’t necessary. There just needs to be 32 characters for the app key which SomeRandomStringWith32Characters is coincidentally 32 characters.