friendsmap | Basic Vue.js app with FirebaseUi auth | Authentication library

It is difficult to exactly say what is your problem based on the error you get (which is not really meaningful! :-) ) but it is probably caused by the fact that userMap is not an iterable.

As you will read in the doc (Section "Only for iterables" at the bottom of the page):

Spread syntax (other than in the case of spread properties) can be applied only to iterable objects.

You can check that userMap is not an iterable with the function you will find in the following SO answer.

The reason is that the Map type in Firestore "represents an object embedded within a document" (as explained in the documentation on data Types) and this Object is actually not a Map stricto sensu, but simply an Object.

As explained in the Map doc (Section "Objects vs. Maps"):

Object is similar to Map: both let you set keys to values, retrieve those values, delete keys, and detect whether something is stored at a key. For this reason (and because there were no built- in alternatives), Objects have been used as Maps historically.

However, there are important differences that make Map preferable in certain cases:

.....

• A Map is an iterable, so it can be directly iterated
• Iterating over an Object requires obtaining its keys in some fashion and iterating over them.

You can check that userMap is actually not a Map by doing

In the ProfileActivity, just find out, if the user you are showing is the logged in user (compare user you get with userKey with your currentUser). If so, hide the sendFriendRequest like so:

You've delcared the classes as inner classes, which might be causing issues. An inner class can only exist within an instance of the enclosing class.

Its probably easier to change them to static classes.

The button should be initialized in viewholder if that is an instance in your recyclerview. Hope the following code will solve your problem.