UX: Generic 40x error when insufficient funds for stamp purchase

[crtahlin]

Problem

When attempting to purchase a postage stamp without sufficient xBZZ/xDAI funds, the UI displays a generic red popup with an unhelpful error message like "error 40x" (HTTP status code).

This provides no actionable information to the user about:

• What went wrong
• Why it failed
• How to fix it

Expected Behavior

The error message should be user-friendly and actionable:

Example improved messages:

• "Insufficient xBZZ balance to purchase stamp. You need X xBZZ but only have Y. [Add funds]"
• "Insufficient xDAI for gas fees. You need approximately X xDAI. [Add funds]"
• "Transaction failed: Not enough funds in wallet 0x... to complete stamp purchase."

Current Behavior

• Red popup appears with generic "Error 40x" or similar HTTP status code
• No indication that the issue is related to wallet balance
• User has to guess what went wrong

Suggested Improvements

1. Parse API error responses - The Bee API returns structured error messages. Parse and display these in human-readable form.

2. Check balances before attempting purchase - Validate wallet has sufficient funds before sending the transaction, and show a clear message if not.

3. Contextual error messages - Map common error scenarios to helpful messages:

   • Insufficient xBZZ → "Need more xBZZ for stamp"
   • Insufficient xDAI → "Need more xDAI for gas"
   • RPC error → "Blockchain connection issue"
   • Stamp depth/amount invalid → Specific validation message

4. Include "next steps" - Each error should suggest what the user can do (e.g., link to faucet, show wallet address to fund, etc.)

Environment

• Swarm Desktop version: 2.6.0
• OS: macOS