Yes. 5xx codes are server errors: The server failed to fulfil a valid-looking request.

5xx · Server errorNot part of the HTTP standard

HTTP 526 Invalid SSL Certificate

Cloudflare: the origin's TLS certificate is invalid.

Example response

HTTP

HTTP/1.1 526 Invalid SSL Certificate
Content-Type: application/json; charset=utf-8

{ "error": "Invalid SSL Certificate" }

Look up the headers shown here in the HTTP headers reference.

What does HTTP 526 mean?: Invalid SSL Certificate. Cloudflare: the origin's TLS certificate is invalid.
Is 526 an error?: Yes. 5xx codes are server errors: The server failed to fulfil a valid-looking request.