This article provides instructions on how to get a FaceTime link in iOS 15 or later. You can send this link to any device (even Android) before making a call.
How to Connect to Someone Using Windows or Android Using FaceTime from an iPhone or iPad | Apple Support
Open the FaceTime app and you should see a Create Link button at the top, on the left side of the screen. Tapping that button will generate a link and activate the Share option. Choose a sharing method, add a message of your choice, and then tap Send.
When you create the FaceTime link, you'll see a green link under FaceTime link that says Add name > Tapping this link will let you give the call you're creating a specific name. For example, if you want to quickly meet someone, you can use the subject of the meeting as the name for the FaceTime call. Then, your recipient can quickly determine the reason for the call.
Yes, you can send a FaceTime link to anyone with an iPhone or Android phone. The instructions above are the easiest way to send a FaceTime link, even to other iPhone users, if you’re not ready to start a FaceTime call with them right away. Once the recipient receives the link, all they have to do is click the link, add a name, and tap Continue to be added to the call.