[Bug] API accepts non-JSON content-type causing parsing errors

[Dev-AdeTutu]

Describe the Bug

API endpoints don't validate Content-Type header. Accepting form-data or plain text as JSON causes confusing parser errors.

Steps to Reproduce

1. POST to /api/payments with Content-Type: text/plain
2. Send JSON body
3. Get 500 error: "Unexpected token in JSON"
4. No clear indication of Content-Type mismatch

Expected Behavior

Validate Content-Type header, return 415 Unsupported Media Type with clear message.

Actual Behavior

Cryptic JSON parsing errors.

Environment

Field	Value
Component	backend / api
OS	Ubuntu 22.04
Network	testnet

[dollfins]

@dollfins has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

hello maintainer, can i work on this issue

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

[Michael997glitch]

@Michael997glitch has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

I’ve resolved similar problems in the past and am confident I can implement a clean, efficient fix quickly,if am given the opportunity.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Michael997glitch to this issue.

[doctorlight0]

@doctorlight0 has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Please consider giving me a chance on this issue. I’ve been trying consistently and would genuinely appreciate the opportunity to prove myself.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @doctorlight0 to this issue.

[utilityjnr]

@utilityjnr has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

i would love to work on this issue

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

[drips-wave]

Congratulations, @utilityjnr! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on August 31, 2026.

🧑‍💻 @utilityjnr: 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 🌊