Notification when Invoice email is opened and/or links clicked by customer?

Notification when Invoice email is opened and/or links clicked by customer?

Since the only way to know when an invoice email has been opened in Zoho Books is by going into the application and hovering over the mail icon in the Invoices section on Zoho Books, my other users never know when it has been viewed.  

I've played with the workflow rules but I can't find any based on signals or email opened so I'm assuming I will need to create a custom function for this? Email notification would probably be easier I'd think but a Cliq notification would also work.

I have never written a Books custom function so any guidance would be appreciated or a template.  I do have Zoho Finance integration with CRM so would doing it through the Books app be the right way to go or should it be in CRM?
      Bootcamp
      Community
      Pricing
      Webinars
      What's New
      Integrations
      Contact Support
      Contact Sales



          Zoho Survey Resources
            Features
            Survey Templates
            Integrations
            Community
            iOS Mobile Surveys
            Pricing
            Android Mobile Surveys
            Insurvey Blogs
            Insight Blogs
            Tips & Tricks





                          Setup Zoho Bigin in 30 Minitues
                          Latest Feature Updates

                            Zoho Desk Resources

                            • Desk Community Learning Series


                            • Digest


                            • Functions


                            • Meetups


                            • Kbase


                            • Resources


                            • Glossary


                            • Desk Marketplace


                            • MVP Corner


                            • Word of the Day




                                Zoho Marketing Automation
                                  Zoho SalesIQ Resources


                                        Manage your brands on social media
                                        Access Zoho Social

                                          Zoho Pagesense Resources


                                                Zoho TeamInbox Resources

                                                  Zoho DataPrep Resources



                                                    Zoho CRM Plus Resources

                                                      Zoho Books Resources


                                                        Zoho Subscriptions Resources

                                                          Zoho Projects Resources


                                                            Zoho Sprints Resources


                                                              Qntrl Resources


                                                                Zoho Creator Resources


                                                                  Zoho WorkDrive Resources



                                                                    Zoho Campaigns Resources

                                                                      Zoho CRM Resources

                                                                      • CRM Community Learning Series

                                                                        CRM Community Learning Series


                                                                      • Tips

                                                                        Tips

                                                                      • Functions

                                                                        Functions

                                                                      • Meetups

                                                                        Meetups

                                                                      • Kbase

                                                                        Kbase

                                                                      • Resources

                                                                        Resources

                                                                      • Digest

                                                                        Digest

                                                                      • CRM Marketplace

                                                                        CRM Marketplace

                                                                      • MVP Corner

                                                                        MVP Corner

                                                                      





                                                                      




                                                                          Design. Discuss. Deliver.

                                                                          Create visually engaging stories with Zoho Show.

                                                                          Get Started Now