My friend and I had the same issue. We spend an ungodly amount of time trying different things. We wanted to play the starter decks against each other. Here is what solved it in the end:
When selecting the decks my friend had the starter decks under "My Decks" as well as "Starter Decks". She had selected them from the "Starter Deck" section, when she instead selected them from "My Decks" instead, the matchmaking was working.

Hope this helps someone save some time.

I have the same issue with a friend of mine.

See attached error screen shots.

Same error - we did note we can against the bot or against random players with custom decks, and it is also possible to challenge friends if you use a stock deck, but you cannot challenge a friend if you are using a custom deck. Very frustrating bug.

consistently unable to play friend challenge. both players get network error cant submit deck and then are soft locked out of playing until restarting the app.

Can't play a direct challenge. It says either "network failure" or "invalid deck".
Version 2022.20.10.4326.963269

Getting the same error. No ghost cards, tried restarting, reinstalling, switching networks, etc. Happens to both players.

It's still not working, please care about that issue, Wizards!

I am not able to play in direct challenge. The error can't submit deck appears each time.

Me too. I cant initiate a brawl direct challenge with two my deck. Opponent doesn't see my request (in direct challenge) or game crash at start (when i choose option through friend list).

Unable to initiate a Brawl Direct Challenge. Everything worked until we tried playing a Yorion Brawl Deck.

****UPDATE: SOLUTION FOUND! Despite the Error saying INVALID DECK, NOT ENOUGH CARDS, Simply being sure there are exactly 60 cards in brawl deck including commander + making sure sideboard is empty = FIXES THE ERROR & LETS YOU USE THE DECK!!!!! ****

A couple weeks ago I could create and play Brawl decks. NOW BRAWL DECKS CANNOT BE CREATED OR EDITED OR ETC.!

For the past week or so unable to create or edit Brawl decks. It allows to you START to create or clone or edit, but when you try to save, it says ERROR - DECK HAS UNDER 60 cards and does NOT save as usable deck.

Brawl is one of my favorites and big reason why I buy gems to get packs and cards.

Please advise- when is Brawl being fixed?

Note: ERROR SAYS BRAWL DECKS INVALID HAVE LESS THAN 60 CARDS - even if 60, 70 or 100 cards and even if a clone of a previously created brawl deck. It always says ERROR INVALID AT LEAST 60 CARDS REQUIRED no matter how many cards are in deck or if it was an old previously fine brawl deck or new deck regardless of commander or cards in deck.

I am on a PC.

Whenever I click on play to join a pvp queue, I get the message "unable to submit deck. Please try later

Whenever I click on play to join a pvp queue, I get the message "unable to submit deck. Please try later

Whenever I click on play to join a pvp queue, I get the message "unable to submit deck. Please try later

When I used M19 Murder, I got error.
I changed M19 Murder to M20 Murder, there was no problem.

When trying to submit a deck to Brawler's Guildhall event, there is an error message saying "network error deck validation failed" even though the deck is legal in the format.

Hello,

For this issue, please submit at: https://mtgarena-support.wizards.com/hc/en-us/requests/new and select 'General Questions'.

Thanks!

I have solved one of the issues here.

I had Murder (Uncommon edition). When I replaced them with the Common edition, it worked.

I get the same response, and there sholud not be anything wrong with the deck (and no, I'm not using Mirage lands).