Rules: How to send an email when an OG membership field changes its value? I have some OG groups in my site. Each group is an online classroom. 

The membership has a few fields (I use the default membership), and one of those fields is a select field with "approved" or "not approved" information about each student's final exam.

I would like to use rules to send an email to each student that change that OG membership field status to "approved". I want this workflow only for users of "exchange-student" role.

But I cannot do that because it seems that I didn't fetched the OG membership. I don't know what I'm doing wrong here.

This is my Rule:

Event:

After updating an existing og membership

Conditions:

Entity exists by property (Parameter: Entity type: OG membership, Property: Exam, Value: Approved)

User has Role
(Parameter: User: [site:current-user], Roles: exchange-student)

Action:
Send a message
(Parameter: Receptáculo: [site:current-user], Private message author: [site:current-user], Private message subject: Aprobaste, Private message body: Mensaje de Prueba)

What am I doing wrong? What am I missing?

Thanks for your help.
I believe the answer lies in your Conditions.

You are checking whether the current user has the appropriate role.

See if you can find a token for the user whose membership has been changed.