How to find threadID in Realtime Database chat query - node.js

Question

I'm working with Firebase Realtime Database and am a fairly new developer. I'm working on a chat application and need to detect which thread to put a message in that comes to a firebase function. The function gets the fromID (sender) and the userID (receiver) and needs to detect which thread belongs to the users.
Issue: The problem is that it successfully detects the thread the first time the message comes in, but then continues afterward - creating a new thread as if the relationship doesn't exist.
Structure:
users
- uid
- threads
- $threadKey
threadMembers
- $threadKey
- members
- $fromID_$userID
Code:
const db2 = admin.database();
db2.ref('users/' + userId + '/threads').once('value').then(snapshot => {
if (!snapshot.exists()) {
console.log("User does not have any threads")
return functions.logger.log('User doesnt have a Thread.');
}
snapshot.forEach((doc) => {
console.log("SNAP : " + doc.key)
checkThreads(doc.key)
})
return functions.logger.log('Finished checking user/uid/threads');
})
function checkThreads(threadId){
const threadRef = db2.ref('threadMembers/' + threadId);
threadRef.once('value', (snapshot) => {
const members = snapshot.child("members").val()
console.log("Members Val: " + members)
if(members == `${fromId}_${userId}` || members == `${userId}_${fromId}`){ //ISSUES WITH REPEATING
console.log("Both users are in the thread")
console.log("Key for thread: " + snapshot.key)
setThread(snapshot.key)
return functions.logger.log('Found membership and set thread');
} else {
const newThreadKey = db2.ref('threads').push().key;
const userThreadRef = db2.ref('users');
userThreadRef.child(fromId + '/threads/' + newThreadKey).set({
timestamp: DBTimestamp.TIMESTAMP
});
userThreadRef.child(userId + '/threads/' + newThreadKey).set({
timestamp: DBTimestamp.TIMESTAMP
});
const threadMembersRef = db2.ref('threadMembers');
threadMembersRef.child(newThreadKey + '/' + userId).set(true);
threadMembersRef.child(newThreadKey + '/' + fromId).set(true);
threadMembersRef.child(newThreadKey + '/members').set(userId + "_" + fromId);
setThread(newThreadKey)
return functions.logger.log('Created membership and set thread');
}
})
}