[Mobile] Add SMS/WhatsApp contribution reminder integration

[Xoulomon]

Suggested Tier: Medium (150 pts)

Description:
Reach low-connectivity users via SMS/WhatsApp reminders, addressing the underbanked target audience.

Tasks:

• Add a backend integration with an SMS/WhatsApp provider (e.g. Twilio)
• Add an opt-in phone number field with OTP verification in the app
• Trigger reminders ahead of deadlines, respecting user-configured lead time
• Add opt-out handling compliant with carrier/WhatsApp policies

Acceptance Criteria:

• OTP verification is required before a number is active for reminders
• Reply-keyword opt-out (e.g. STOP) is honored within one reminder cycle

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[Luchistack]

@Luchistack has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hi! I’m a full-stack developer with a strong blockchain background. I’d love to handle this issue and can deliver a clean, reliable solution. Kindly assign it to me.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Luchistack to this issue.

[drips-wave]

Congratulations, @SIMPLE-koder! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 30, 2026.

🧑‍💻 @SIMPLE-koder: Please resolve the issue such that the repo's maintainers have enough time to review your contribution before the due date. You'll earn Points for completing the issue on-time, which will make you eligible for a share of the Stellar Wave Program's reward pool.

Warning

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🤠 Repo maintainers: Please keep an eye on the contributor's progress and review their work before the due date. You can manage this issue, including adjusting its complexity and points, here.

🌊 Happy Wave 🌊

[drips-wave]

Congratulations, @cynthiaCODE01! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 30, 2026.

🧑‍💻 @cynthiaCODE01: Please resolve the issue such that the repo's maintainers have enough time to review your contribution before the due date. You'll earn Points for completing the issue on-time, which will make you eligible for a share of the Stellar Wave Program's reward pool.

Warning

When opening a PR, please link it to this issue to ensure it gets tracked accurately. Points are awarded when this issue is marked as completed by the maintainer.

🤠 Repo maintainers: Please keep an eye on the contributor's progress and review their work before the due date. You can manage this issue, including adjusting its complexity and points, here.

🌊 Happy Wave 🌊

[drips-wave]

This issue is assigned to @cynthiaCODE01 via the Stellar Wave Program.

Other assignees have been removed. To reassign, please unassign the current contributor through Drips Wave first.