Thanks. I have tested and something seems to be wrong.
When I did the v5 migration I setup mail and sent a test and it worked but now, for some unknown reason emails are not being sent.
I went to: Settings // Email Settings and it was set to “Default” but when I tried to send an invoice I got the error “Something went wrong” so I changed the email settings to SMTP and completed the credentials and sent a test mail and that was received. But when I opened the invoice and clicked “Send Invoice” I got the same error: “Something went wrong”.