Will my ex know my message is coming from an app?

No. When you send a message through the BestInterest app, and your coparent is not a user of BestInterest, they will receive your just like a regular SMS message. There is no branding or indication that the message was sent from an app. They will not know it is being sent by you using an app.

When they reply, their message will be processed by BestInterest and displayed in the app.

Your ex will not know it was sent through BestInterest unless you choose to tell them. This allows you to manage your communication in a more organized and child-focused way, while ensuring that your coparent continues to receive messages in a familiar format.

If your coparent decides to join BestInterest, both of you can communicate directly within the app in Together Mode, but until then, it will look like a regular SMS on their end.