I need to do a link witch can start a process model. How I can do this?

I tried your use case and its possible to provide the action URL on the Email message body.
For Example : The URL for "Apply Leave" Process is dev.appiancloud.com/.../abc1234, then you can provide the same in the configuration of the message body of the "Send Email" smart service, and the user will be prompted to the Action's form.
We need to make sure that the URL should be updated with respect to different environments.
To do things we can make it possible but its better to consider the Appian best practices, not sure if this one's allowed.

I tried your use case and its possible to provide the action URL on the Email message body.
For Example : The URL for "Apply Leave" Process is dev.appiancloud.com/.../abc1234, then you can provide the same in the configuration of the message body of the "Send Email" smart service, and the user will be prompted to the Action's form.
We need to make sure that the URL should be updated with respect to different environments.
To do things we can make it possible but its better to consider the Appian best practices, not sure if this one's allowed.