fix: accept the INSTALLMENT_SELECT next action type

[jimmyn]

Depends on MONEI/monei-openapi-schema#161. Regenerated from that branch (build:local).

Why: the API returns nextAction.type = INSTALLMENT_SELECT for card payments eligible for MONEI Flex. PaymentNextAction raised ApiValueError on it, so payments.get() and webhook parsing failed for those payments.

Change: the enum value in PaymentNextAction, plus a test that deserializes such a payment through ApiClient.deserialize (fails on master with the error above).

Verification: uv run pytest 266 passed. Formatted with the pinned uv run black (25.1). build.sh calls the global black; a newer one also rewrote __init__.py, configuration.py and rest.py (blank lines only). Those are left out.

Summary by CodeRabbit

• New Features
  • Payment flows can now support an installment selection step, allowing customers to choose between paying in full or in installments on the payment page.

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

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Run ID: 34635aa7-6211-4ae4-85af-457509870a00

📥 Commits

Reviewing files that changed from the base of the PR and between 04e60a3 and b359c24.

📒 Files selected for processing (2)

• Monei/model/payment_next_action.py
• test/test_payment_next_action.py

🔗 Linked repositories identified

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• MONEI/common (manual)

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📝 Walkthrough

Walkthrough

PaymentNextAction now accepts and documents INSTALLMENT_SELECT. A test deserializes a payment response with this action type and checks that next_action does not contain must_redirect.

Changes

Installment selection next action

Layer / File(s)	Summary
Next action type and deserialization test Monei/model/payment_next_action.py, test/test_payment_next_action.py	PaymentNextAction adds INSTALLMENT_SELECT to its allowed types and documents the payment choice at redirectUrl. The test checks the deserialized action type and confirms that next_action does not contain must_redirect.

Priority: ➖ Normal

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix

Merge Risk: ⚪ Minimal · up to b359c

No concrete failure in the installment-selection change is established; the supplied test covers deserialization of the new action type.

🚥 Pre-merge checks | ✅ 2

✅ Passed checks (2 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

✨ Simplify code

• Commit to this branch
• Create a new PR

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