This is a compliance CSID (CCSID) that is issued by the einvoicing system as it is a prerequisite to complete the compliance steps. The CCSID is sent in the authentication certificate header in the compliance api calls.
The CSR specification required to perform the Compliance API call is covered in section 4.3 of the Developer Portal user manual. Start Onboarding your system point of sale POS and Link with Zakat, Tax and Customs Authority Saudi Arabian, Here you can Create and Build a Digital Signature ECDSA Certificate Online OpenSSL (CSR and Private Key) and Compliance XML Files Standard and Simplified) and Compliance CSR to Get Authorizationa and Depending on your place in the onboarding process, create a Compliance CSID (CCSID) or a Production CSID (PCSID). Compliance CSID