# Processing Flow

When the form is submitted the system performs the following steps:

1. **Determine Page**: Identify which page the submitted data belongs to.
2. **Precondition Check**: Verify the page's preconditions. If preconditions are not met, the user is redirected to the appropriate page.
3. **Data Validation**: Validate the submitted data according to the page rules.
   * In case of invalid data, return error messages
   * If data is valid, update the checkout state
4. **Apply Campaigns**: After data validation, recalculate applicable campaigns and discounts.
5. Determine Next Page: After a successful operation, the response includes the next page information within the page context, indicating which step the user should proceed to.


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