turnstile: document error 200500 (#23417)

* turnstile: document error 200500

* update wording slightly

Author: Le0Developer

src/content/docs/turnstile/troubleshooting/client-side-errors/error-codes.mdx

@@ -31,9 +31,10 @@ When an error code is marked with `***`, it means that the remaining numbers can
 | `120***`                                        | Internal Errors for Cloudflare Employees.                                                                                                                                                                                   | No    | Only encountered by Cloudflare Support Engineers while debugging.                                                                                                                                                                                                         |
 | `200010`                                        | Invalid caching: Some portion of Turnstile was accidentally cached.                                                                                                                                                         | No    | Encourage the visitor to clear their cache.                                                                                                                                                                                                                               |
 | `200100`                                        | Time problem: The visitor's clock is incorrect.                                                                                                                                                                             | No    | Encourage the visitor to set their clock to the correct time.                                                                                                                                                                                                             |
+| `200500`                                        | Loading error: The iframe under challenges.cloudflare.com could not be loaded.                                                                                                                                              | No    | Ensure your [Content Security Policy](/turnstile/reference/content-security-policy/) allows this or encourage the visitor to reduce their security preferences in case their user-agent is blocking third-party iframes.                                                  |
 | `300***`                                        | Generic client execution error: An unspecified error occurred in the visitor while they were solving a challenge.                                                                                                           | Yes   | Potentially an automated visitor. Retry the challenge. Upon multiple subsequent failures, verify the visitor otherwise.                                                                                                                                                   |
 | `400020`                                        | Invalid sitekey: The sitekey is invalid or does not exist.                                                                                                                                                                  | No    | Ensure that the sitekey is valid and exists.                                                                                                                                                                                                                              |
-| `400030`                                        | Invalid size: The provided size is not a valid option.                                                                                                                                                                      | No    | Ensure that the size is one of the [valid options](/turnstile/get-started/client-side-rendering/#widget-size).                                                                                                                                                             |
+| `400030`                                        | Invalid size: The provided size is not a valid option.                                                                                                                                                                      | No    | Ensure that the size is one of the [valid options](/turnstile/get-started/client-side-rendering/#widget-size).                                                                                                                                                            |
 | `400040`                                        | Invalid theme: The provided theme is not a valid option.                                                                                                                                                                    | No    | Ensure that the theme is either `light`, `dark` or `auto`.                                                                                                                                                                                                                |
 | `600***`                                        | Challenge execution failure: A visitor failed to solve a Turnstile Challenge. Also used by [failing testing sitekey](/turnstile/troubleshooting/testing/).                                                                  | Yes   | Potentially an automated visitor. Retry the challenge. Upon multiple subsequent failures, verify the visitor otherwise.                                                                                                                                                   |