whereClause syntax

I have some related data
Centers which has certain specialties(boolean values)
so I want to retrieve only the centers that have a certain speciality = true;
I proposed many whereClause but nothing worked
I attached the necessary files for the full understanding
Please provide me with a proper syntax

Here is cURL to get Center objects with sports speciality

curl -X GET -H ‘application-id:XXX’ -H ‘secret-key:XXX’ https://api.backendless.com/v1/data/Center?where=specialities.sports%3Dtrue

See Loading a Subset of Related Child Objects section in the documentation

I still don’t get it

Can you just write the whereClause for my case as i described above

The where clause is already in Vitaly’s response:

[url=https://api.backendless.com/v1/data/Center?where=specialities.sports%3Dtrue]specialities.sports=true[/url]