delete https://test.bitpay.com/tokens//sins/
This endpoint allows you to unlink a SIN (SIN1) from an approved API token, as long as another SIN (SIN2) has first been linked to this same token. Once executed, the private key corresponding to SIN1 removed cannot be used anymore in combination with the approved API token.
If you intend to remove SIN1 from a given token, this request would need to be authenticated using the public key pair corresponding to SIN2.