Hi @JK ,
Welcome to Microsoft Q&A Platform. Thank you for posting query here.
It seems Azure data factory uses by default TLS version 1.2 for data encryption in Transit. Click here to know more about it.
Please check below link to know about Security considerations for data movement in Azure Data Factory.
May be you can try prefix https:// in REST endpoint and see if that works? Also, Please try to enable "Server certification validation" inside linked service and see?
Please let us know how it goes and please share error message details if any. Thank you.