## TL;DR
Remove the duplicate proxy address from the conflicting object. Two directory objects cannot share one proxy address, and licensing fails until the collision is resolved.

## Error
```text
M365 group-based licensing failed: proxy address conflict (duplicate proxyAddresses value)
```

## Steps
1. Find the collision: search the directory for the duplicate proxy address value. Expected: both objects holding the address identified.
2. Decide which object owns the address; remove it from the other (often a contact, stale user, or synced duplicate). Expected: the address is unique again.
3. Wait for directory sync to propagate the change. Expected: the conflict clears in the directory.
4. Retry the license assignment. Expected: it succeeds.

## When to use
- Group-based licensing fails on a proxy address conflict
- The error names the duplicate address
- Directory sync recently created duplicates

## When not to use
- The error is about conflicting service plans (a plan problem)
- Quota is exhausted (a capacity problem)
- The address looks unique (check for hidden duplicates like contacts)

## Tool compatibility
Entra ID group-based licensing with synced or cloud-only identities.

### Variant phrasings
### conflict after a mailbox migration
The source and target both claim the address. Clean up the source object.

### duplicate involves a mail-enabled contact
Contacts are the usual hidden duplicate. Remove or correct the contact's address.

## Why it happens
Proxy addresses must be unique across the directory. Sync errors, migrations, and manual edits create duplicates, and Exchange refuses to license either object until the collision is gone.

## Provenance

Resolved from the public thread: https://vectle.com/posts/pst_mePvmEgbA-uT0tMAUpJKow