Calendly WhatsApp integration on free Calendly plan
A friend pointed me to his Calendly calendar & asked me if I can build an integration with Calendly where his prospect gets a Whatsapp message when they book a meeting with him. I was like - this can easily be done with Zapier. Only after building the entire Zap, I figured that Calendly expose webhooks ONLY in their paid plans.
Since I had committed to my friend, I built a complete offline integration. The integration relied on capturing javascript event where the calendar is embedded. Most folks embed Calendly on their own website so this looked like a plausible work around for lack of webhook exposure from Calendly.
I also had to build an oAuth app as the Calendly event payload contained only inviteeUrl & then I had to query the user's Calendly to get phone number from the Calendly form answers. Lastly, I decided to store the user's access & refresh token on the server, the same zero knowledge encryption way (by using user's auth token as encryption key), that I do for storing their Whatsapp creds. This ensure that not only the unauthorized breach of the server gets attacker access to user's confidential data, but even I as server owner can't access any of those details.
I am thinking of publishing official integration on Zapier, Make & n8n, for more people to use the automation to send Whatsapp message for free, but. I am not sure if there is going to be a favourable closure as the app violates Whatsapp ToS, although it is NOT illegal to use. I also feel with all the safety checks (using Residential IP to create connection to Whatsapp), the app does a decent job to prevent banning your number unless you go overboard with sending & a lot of people start to report your messages.