Is there an API to upload my own certificate for website?

Hi, @yangzhaofeng. Yes, there is an API endpoint to update SSL certificates for sites. There is some information about the endpoint here:

https://open-api.netlify.com/#tag/sniCertificate/operation/provisionSiteTLSCertificate

This support guide about reverse engineering our API might also be helpful:

​Please let us know if there are other questions.