I wish I could make it better, @Wai Sum Chong.
Currently, we have an on-going issue where the clients from our customers, like you, didn't receive the emailed invoice. Rest assured that we've already informed our engineering team and they're in all hands working to fix this as soon as possible.
With that being said, I'd recommend contacting our Customer Care Support so you'll be added to the list of affected users. Once added, you'll receive all available updates about this on-going issue via email message. To do so, here's an article you can read for their contact details: Contact QuickBooks Self-Employed Support.
With their tools, a specialist can pull up your account, securely, and share the appropriate resolution while waiting for the suggestions from our engineering team.
Lastly, I've also included this helpful article for ideas about invoicing and its related functions: Create invoices in QuickBooks Self-Employed.
We appreciate your patience as we're working on this. Please let me know in the comments if you have any other questions.