Registration submission fails: self-service/registration returns 500 HTML error page

Error

ResponseError: The Ory API endpoint returned an unexpected HTML or text response. Check your console output for details.

Stack trace

<anonymous> (@ory/elements-react/src/util/sdk-helpers/utils.ts:191)
  ← sO / onSubmitRegistration (@ory/elements-react/src/util/onSubmitRegistration.ts:39)
  ← <anonymous> / useOryFormSubmit (@ory/elements-react/src/components/form/useOryFormSubmit.ts:124)
  ← <anonymous> / react-hook-form createFormControl.ts:1614

Source (node_modules/@ory/elements-react/src/util/sdk-helpers/utils.ts:186-196)

      contentType.includes("text/") ||
      contentType.includes("html") ||
      contentType.includes("xml")
    ) {
      // Handle human-readable content
      await logResponseError(err.response, true)
      throw new ResponseError(
        err.response,
        `The Ory API endpoint returned an unexpected HTML or text response. Check your console output for details.`,
      )
    }

Request context

• URL: https://main.devguard.org/registration?flow=b4e9c21d-2488-40f3-9f1d-3e9813e58352
• Culprit route: /registration
• User submitted the registration form (name, email, confirmed-terms checkbox, submit) after which POST https://main.devguard.org/self-service/registration?flow=b4e9c21d-2488-40f3-9f1d-3e9813e58352 returned 500 with an HTML/text body instead of JSON, which the Ory Elements SDK can't decode ("Unable to decode API response").
• A React error #418 (hydration mismatch) was also logged as a breadcrumb on page load, ~24s before the form submission — same recurring issue as issue 3305 and related issues.
• User agent: HeadlessChrome — likely an automated/synthetic test rather than a real user, but the underlying 500 on registration submit would affect real users too.

GlitchTip

• Issue: https://error-tracking.devguard.org/devguard/issues/3829
• Event ID: 019fc7006be971ecb22da2d43de04bf8
• First seen: 2026-08-03T09:42:01.346Z

Start by reproducing the POST to /self-service/registration from the reported /registration flow and inspect the GlitchTip event and server response. Read the SDK handling in node_modules/@ory/elements-react/src/util/sdk-helpers/utils.ts and the cited onSubmitRegistration.ts path to understand the failure boundary. Done means registration no longer returns a 500 HTML/text response and the form receives the expected API response.