Before sending invoices from Simplicate, it's wise to first set up where an invoice should be sent. You can do this in CRM > Invoicing > Invoicing Preferences.
After you have correctly configured this for all your clients, you are ready to send invoices.
To send invoices collectively, go to Invoices > Draft Invoices.
You can now select all invoices that are ready under draft invoices (step 1 in the image below):
Select all draft invoices at once: Check the top box.
Select a few invoices: Only check those draft invoices.
Once you have checked the invoices you want to send at once, click on Actions > Send via email (step 2 in the image below).
As soon as you click on "Send via email", the following pop-up will appear:
No: You will return to the previous screen.
Yes: All selected invoices will be sent at once.