Add SDK method for `updateFeeRate` and `updateMaxDiscount`

[Levi-Ojukwu]

Description:

The contract has admin functions for fee and discount configuration that need SDK wrappers.

Why it matters: Fee configuration affects protocol economics.

Acceptance Criteria:

• Create updateFeeRate(rate) admin method
• Create updateMaxDiscount(rate) admin method
• Add tests

Relevant Files: contracts/invoice_liquidity/src/lib.rs:227-282, sdk/src/index.ts

---

[ABEEGOLD]

Hi, I'd like to work on this issue. I have experience wiring TypeScript SDK wrappers to Soroban admin functions.

My plan: implement updateFeeRate(rate) and updateMaxDiscount(rate) in sdk/src/index.ts, wired to the existing admin logic in contracts/invoice_liquidity/src/lib.rs (lines 227–282), and add tests covering both valid updates and rejection for unauthorized callers or out-of-range values.

Happy to get started right away.

[Heazzy500]

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[Yinklekay]

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I love to work on this issue

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[thegreatfeez]

@thegreatfeez has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

Hello, i would like to work on this issue

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Congratulations, @thegreatfeez! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on July 30, 2026.

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[grantfox-oss]

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Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #515)
2. Your PR will be reviewed by the Invoice-Liquidity-Network maintainers

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This issue has been completed by @thegreatfeez as part of the Stellar Wave Program's 7th Wave 🥳

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