Hi,
Unfortunately is not possible to use attributes as value for the event’s parameters.
If you try to track these values on Facebook, there might be some workaround:
1. Add the value as a product tag. Product tags are automatically tracked by all our default events.
2. Create a Custom Audience or Custom Conversion using the appropriate event and the tag value.
EXAMPLE:
Let’s say you want to retarget clients that bought products with a “red hat” tag.
You need to create a Custom Audience based on the Purchase event where the custom attribute tag=red hat.
We don’t track tags for Google’s events, because of their more strict events’ structure.