This is important for one of the marketing departments that i work for.
WhatsApp link doesn’t support UTM tracking. To track where WhatsApp leads are generated through WhatsApp link, we create a unique reference / pre-filled message for each source / website like: "Message sent from x.com:"
Then, add them to the pre-filled message of the WhatsApp link. The tracking method only works if the customers use the existing custom pre-filled message, and fortunately most of them keep it as it's usually easier for them to leave it as it is and add their message after it than to remove and re-write a new message from scratch.
My customer paid for the annual subscription of Buttonizer, and now they want to switch back to the previous/traditional link with prefilled message (like https://wa.me/37666666?text=Message%20Sent%20from%20websiteX.com:%0A) because it was providing them with more information.
I find Buttonizer very useful because first the visitors invests a time in writing, then they just click to send, but for the moment it lacks the "pre-filled / tracking" feature that is important for my customer.
So, unfortunately i will have to swith back to the pre-filled message solution, and come back to buttonizer as soon as you allow this feature... :.(