PeaceMaker,
Thank you for your attention and explanation. Not wanting to abuse your goodwill, any codes for study?
I read in an article that individual identifiers could be used, I don't know if this is correct, instead of those provided by the FCM. In my case, I could use the customers' phone number as this ID, because one of the business rules is that the customer enters their phone number in the application (I don't intend to do an automatic search, because I've read elsewhere that the Google has already created restrictions for this method).
And of course the number will be encrypted. But, it is an identifier.
If this is possible, I believe that my search, now, is how to send the push message to the client via FCM, using this identifier as a parameter.