Facebook Pixel displays 'custom_data' with '_removed_' value

I'm using ember-metrics to send custom event to Facebook Pixel. This is my code:

this.get('metrics').trackEvent('FacebookPixel', {event:'FreeTrial', custom_data: { location:location, url:'free-trial', campaign:campaign}});

When I go to Facebook control panel I see the following:

Nov 11, 2019, 9:53 AM
iPhone
custom_data:_removed_,

Facebook have the following help pop-up for this field: The parameters sent with this event. Parameter values may be removed if they were hashed before being sent to Facebook, or contain sensitive information that we detect.

Anyone had this issue before? What am I doing entirely wrong?