Terminal and merchant resolution rules

For routes that use transaction or report request bodies, terminal and merchant are resolved in this order:

1. Use terminal from the request if provided.
2. If not provided, use the currently selected terminal (session/default context).
3. If still not available, use the first configured terminal.
4. For merchant, use request value if provided.
5. If not provided, use the default merchant for the resolved terminal.

Important behavior:

• merchant is always resolved for the final terminal.
• If a requested or resolved terminal has no valid merchant, the request fails.
• If no terminal can be resolved, the request fails.
• If you send both fields, they must represent a valid pair in current configuration.

Integration recommendation:

• Use /terminals response as the source of valid terminal + merchant combinations.