# The chat app

> Models, cost per reply, paying with credits or USDC, and the wallet panel in the web, desktop and mobile apps.

Section: Using Katara. Web page: https://docs.katara.com/customers/chat-app/

## Choosing a model

The picker in the header lists every model Katara can serve. Each entry is a bundle (see [Models and bundles](https://docs.katara.com/concepts/models.txt)). The default is a managed model that always answers; marketplace models may be cheaper or faster when providers are online.

## What a reply costs

Under every reply is its cost, in Credits for a reply paid with credits or in USDC for one paid from your wallet, and, on hover, who served it, including which model Katara Cortex picked. Replies answered by a managed vendor are marked. Costs are also in your usage history.

## Questions about Katara

Ask about Katara itself, such as pricing, credits or running a provider, and the app answers from these docs and katara.com and links the pages it used. The question is looked up on Katara's servers and the matching pages are added to the request, so they count toward the reply's input tokens.

## The balance

The header shows the balance that pays for your next message: your Credits or your spendable USDC. Click it to switch between them. A new account starts on credits, with a signup credit; buy more by card under **Billing** in the portal. Paying with USDC needs a wallet, and when something needs doing first, the header says so: create a wallet, approve spending, or add funds.

Replies paid with credits or USDC can run on independent providers in Katara Community as well as Katara's own models, unless you turn it off. A reply paid with credits costs the same credits either way. With it on, Community providers are tried first, and their replies may take longer to start.

## The wallet panel

Paying with USDC uses your wallet on Live, on Avalanche C-Chain. Under **Account → Wallet**:

- **Balance and next step.** Spendable, your wallet balance, your prepaid balance, and the amount you approved; your address with a copy button; the spending approval and when it ends; a withdrawal button for the prepaid balance.
- **Add funds.** Your address and a QR code, for a transfer of USDC on Avalanche C-Chain.
- **Budget.** Follow the balance, or cap the approved amount. The approval period is 30 days, 6 months, or a year.

## Desktop and phone

The desktop app has the same wallet panel under **Settings → Wallet**, and the same cost line under each reply.

On the phone, the wallet card under **Settings** shows the balance and sets the budget. Creating a wallet and approving spending need your passkey, which lives in the browser, so those two buttons open the portal; come back to the app when you are done.

## Errors you may see

- *Paying with USDC is paused until you approve spending.* Open the wallet panel and approve, or switch the header to Credits.
- *Your spendable balance is below this request's maximum charge.* Add funds or raise the cap, or switch the header to Credits. Long prompts and large `max_tokens` raise the maximum.
- *Insufficient credits.* Add credits under **Billing** in the portal, or switch the header to USDC.
- *No provider can take this request right now.* Try again shortly. With Katara Cortex selected this is rare; a named model shows it whenever its providers are away.