Firebase serialization names

The Firebase SDK uses the annotation it finds for the property whenever it gets or sets its value. That means you need to consider how Firebase gets/sets the value, and annotate each place it looks.

Since you're declaring a getter method, Firebase will use that to get the value of the property. It will use the field for setting the value. So the annotation needs to be on both:

public class Pojo {
   @PropertyName("Guid")
   public String guid;

   @PropertyName("Name")
   public String name;

   @PropertyName("Guid")
   public String getPojoGuid() {
       return guid;
   }

   @PropertyName("Guid")
   public void setPojoGuid(String guid) {
       this.guid = guid;
   }
}

If you'd have getters and setters, the annotation would need to be on those, but not on the fields anymore:

public class Pojo {
   private String guid;
   private String name;

   @PropertyName("Guid")
   public String getPojoGuid() {
       return guid;
   }

   @PropertyName("Guid")
   public void setPojoGuid(String value) {
       guid = value;
   }

   @PropertyName("Name")
   public void setPojoGuid(String guid) {
       this.guid = guid;
   }

   @PropertyName("Name")
   public void setPojoGuid(String value) {
       name = value;
   }
}

@PropertyName :

Marks a field to be renamed when serialized. link

you have to use @PropertyName with public fields and no need for getters/setters

What you are looking for is the feature of SDK Version 9.2 in which you can now use a new @PropertyName attribute to specify the name to use when serializing a field from a Java model class to the database. This replaces the @JsonProperty attribute.

@PropertyName("Username")
public String username;
@PropertyName("Email")
public String email;

See also this post in which Frank van Puffelen explains very clearly this concept.