Cannot upload Custom Page "Must be larger than 100 characters)

I am receiving the error "Your custom page must be larger than 100 characters (Code: 1203)"

I’m using the “::IM_UNDER_ATTACK_BOX::” in the HTML. My HTML has no errors as checked by a W3 validator. Yet I cannot upload any custom error page. The url is also correct because I can visit the page on my site with no errors.

This has come up before: (EDIT: oops…not quite like this)

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You linked a post, the answer to that posts links 2 other posts. None of which are about the specific error message “Must be larger than 100 character”

The first post is regarding exceeding the character limit (not being below it)
The second post is regarding having a missing token, none which can help solve my issue.

Some troubleshooting tips here,

One suggestion is to run it through the HTML validator. Past instances of the 1203 error (did you get that code?) have been caused by warnings and errors.

I already have, there are no errors. And yes I got error 1203

Can you let support know? To contact Cloudflare Customer Support, login & go to and select get more help. Please give Support the complete details and link to your Community post.

That sound similar to a recent issues with a 403 that was throwing the error. The team is aware and working on that.

(You can test that yourself if you flatten/inline all the documents for the custom error page into a single file (including images), we use these) :

If related, you’ll see

Response code 403 (Forbidden)
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I let support know, not sure what’s causing it. Since it was working before with the same error page html file.

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Perfect, thank you. I see the ticket and have added myself to it. Can you respond back to the engineer with the location details? Thank you & sorry for the trouble.

I had a firewall rule which forces a JS challenge on all users (that do not equal a certain random threat score)

Temporarily disabling this rule fixed the problem and I was able to upload the custom page again.


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