A 401 from HTML/CSS to Image usually means the request’s authentication data was missing, incorrect, disabled, or—if you are using a signed image URL—does not match the exact query string. For the standard API, send the matching API ID as the HTTP Basic username and API key as the password. A 403 is different: credentials may be valid, but the key lacks permission or the operation is not available on the plan.
First identify which authentication method your request uses
HTML/CSS to Image has two relevant request patterns. Standard image creation sends a POST request to https://hcti.io/v1/image and authenticates with HTTP Basic. A signed create-and-render URL carries a signature derived from its query string. Diagnose the method actually used; changing Basic credentials will not fix a bad signed URL, and recomputing a URL signature will not fix a bad Basic credential pair.
| Request type | Authentication | First 401 check |
|---|---|---|
| Standard API request | HTTP Basic: API ID is username; API key is password | Confirm the matching pair is correct and the key is enabled. HTML/CSS to Image API key documentation |
| Signed image URL | HMAC SHA-256 token calculated from the query string using the API key as the secret | Recalculate the token from the exact query string and confirm the key is enabled and permits images:create. HTML/CSS to Image signed URL documentation |
Fix a 401 on a standard API request
- Check that both credentials belong together. The API ID is the Basic username and the API key is the password. Copy both from the same intended organization or account; an ID paired with another key will not authenticate.
- Confirm the key is enabled. Check the key controls in the HTML/CSS to Image account. A disabled key cannot authenticate, even when its value is otherwise correct. The vendor’s API key guide covers key management at Using the API.
- Inspect the Authorization header construction. Basic authentication encodes
API_ID:API_KEYusing Base64 and sends it as the Basic Authorization credential. Ensure there is a colon between the two values before encoding, and do not accidentally include surrounding whitespace or line breaks. - Keep the key on a server. Do not place the API key in browser JavaScript, a public repository, or a screenshot of a debug log. HTML/CSS to Image’s documentation says, “Treat your API Key like a password.” If a key has been exposed, disable or replace it rather than continuing to use it.
The vendor’s JavaScript example constructs the Basic Authorization value from the API ID and key; see its JavaScript example. Compare your request with the vendor’s documented example for the language or client you use, and inspect the outgoing request without printing the secret itself. A 401 response alone does not prove which of these checks failed, so use the response body and actual request construction to narrow it down.
Fix a 401 on a signed image URL
Signed URL authentication does not use the API ID as a Basic username. Its token is an HMAC SHA-256 hash of the query string without the leading ?, with the API key as the signing secret. A valid token therefore depends on the exact string that is signed.
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- Rebuild the signature from the exact query string that will appear in the URL, omitting only the initial question mark.
- Preserve parameter order, URL encoding, and whitespace exactly. Changing the order or encoding after signing changes the input and invalidates the signature.
- Use the API key as the HMAC secret, and verify that the key is enabled and grants
images:create. - If any parameter changes, generate a new token. Do not reuse a signature for a modified URL.
See the vendor’s signed URL guide for its signing requirements. Keep the signing key private: a signed URL contains a token, but that does not make it safe to expose the underlying API key.
Know when the response is 403, not 401
HTML/CSS to Image distinguishes authentication from authorization. Its API guidance describes 401 for missing or invalid credentials and 403 when credentials are accepted but the required permission is absent. Check the response body for the permission it names, confirm the key belongs to the organization that owns the resource, and check whether the operation is eligible under your plan. Granting a permission may not remove a plan restriction. See the vendor’s permissions documentation.
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- 401: investigate the Basic ID/key pair and key state, or the signed URL’s exact input and token.
- 403: investigate permissions, organization ownership, and plan eligibility.
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When to contact support
If the request method, credential pair or signature, key state, and—where relevant—permissions and plan eligibility all check out, use the response body and a redacted request description when contacting support@htmlcsstoimage.com. Never send the API key in email or chat.
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