Fix hardcoded FX rate in fiat withdrawal service

[dotunv]

Description

The fiat withdrawal service uses a hardcoded exchange rate instead of the live FX service:

File: internal/fiat/service.go (line 100)

rate := decimal.NewFromInt(1500) // 1 USDC = 1500 NGN

Impact

• Withdrawals use an outdated/inaccurate exchange rate
• Users may receive incorrect fiat amounts
• The FX service exists but is not used in this flow

Proposed Fix

Replace the hardcoded rate with a call to the FX service:

quote, err := fxService.GetQuote(ctx, "USDC", "NGN", amount)
rate := quote.Rate

Acceptance Criteria

• Fiat withdrawals use live FX rates
• Hardcoded rate is removed
• Error handling for FX service failures
• Tests verify correct rate usage

Labels

bug backend

[Okorie2000-code]

Hi Maintainer, I'd love to work on this issue. I understand the requirements and will submit a clean, well-tested PR within 24hrs. Please assign it to me

[retkatmun]

Hi,

I’m a full-stack software engineer with experience building scalable web apps, backend systems,

I’d love to work on this issue. I’ve reviewed the requirements and have a clear implementation plan to deliver a clean, well-tested solution that meets all acceptance criteria and aligns with the project’s standards.

I can start immediately and provide timely updates throughout the implementation.