The microflow name is not just “ACT_CheckLogin” but it includes the module name e.g. “MyModule.ACT_CheckLogin”
The context parameter you can leave out and the origin should be something like “this.mxform”
Also, make sure to call resolve and reject in the callback and error respectively.
You can pass a Nanoflow as a parameter as shown below. And also refer the details in this link.
I wrote an article on this a while back as this changed in Mendix 8.7.
Hope this also helps.
Before it was a bit harder, to get the nanoflow exported, it required a helper widget
Alternatively, you could also return the date from the the JS action and call a sub nanoflow (now supported) with the data of your custom action.