The entityProperties is an array of objects which can be used to carry any type of information and then it is saved as entity properties for an issue.
How to Sync EntityProperties
Basically, to synchronize entity properties between issues add the following code:
Here is an example of adding to entityProperties a custom value:
On the remote side, it's possible to add logic. In this case, the property "mood" will be also added to the entity properties of the issue: