We also recommend a consistent way of informing callers when they do not include the required KYAPay token in their requests.

When a KYAPay token is missing
- Return an HTTP 402 Status Code
- In the body include a message on how to create these tokens e.g. ERROR: Missing KYAPay token in the skyfire-pay-id header. Please create an account at https://app.skyfire.xyz and create a kya | pay | kya+pay token - https://docs.skyfire.xyz/reference/create-token and include it in your request in the skyfire-pay-id header.
When a KYAPay token is invalid
- Return an HTTP 402 Status Code
- In the body include a message on how to create these tokens e.g. ERROR: Missing KYAPay token in the skyfire-pay-id header. Please create an account at https://app.skyfire.xyz and create a kya | pay | kya+pay token - https://docs.skyfire.xyz/reference/create-token and include it in your request in the skyfire-pay-id header.
Specifically when a pay token is missing
- Return an HTTP 402 Status Code
- In the body include a message on how to create these tokens e.g. ERROR: Missing pay token in the skyfire-pay-id header. Please create an account at https://app.skyfire.xyz and create a pay token - https://docs.skyfire.xyz/reference/create-token and include it in your request in the skyfire-pay-id header. The required amount is ...
Specifically when a pay token is depleted
- Return an HTTP 402 Status Code
- In the body include a message e.g. ERROR: The given pay token is depleted. Please create and send a new pay token. The required amount is ...

Formatting

If you believe the caller to be a Web Scraper, you may prefer to return the above messages in plain text
If you believe the caller to be an LLM, you may prefer to return the above messages in a structured JSON format e.g. https://modelcontextprotocol.io/specification/2025-06-18/server/tools#error-handling

llms.txt

We also recommend adding an llms.txt file to your website that includes an explanation of your use of KYAPay tokens.