code: func (c *ACMPCA) UntagCertificateAuthority(input *UntagCertificateAuthorityInput) (*UntagCertificateAuthorityOutput, error) {
  	req, out := c.UntagCertificateAuthorityRequest(input)
  	return out, req.Send()
  }
docs: // UntagCertificateAuthority API operation for AWS Certificate Manager Private Certificate Authority.
  //
  // Remove one or more tags from your private CA. A tag consists of a key-value
  // pair. If you do not specify the value portion of the tag when calling this
  // operation, the tag will be removed regardless of value. If you specify a
  // value, the tag is removed only if it is associated with the specified value.
  // To add tags to a private CA, use the TagCertificateAuthority. Call the ListTags
  // operation to see what tags are associated with your CA.
  //
  // Returns awserr.Error for service API and SDK errors. Use runtime type assertions
  // with awserr.Error's Code and Message methods to get detailed information about
  // the error.
  //
  // See the AWS API reference guide for AWS Certificate Manager Private Certificate Authority's
  // API operation UntagCertificateAuthority for usage and error information.
  //
  // Returned Error Codes:
  //   * ErrCodeResourceNotFoundException "ResourceNotFoundException"
  //   A resource such as a private CA, S3 bucket, certificate, or audit report
  //   cannot be found.
  //
  //   * ErrCodeInvalidArnException "InvalidArnException"
  //   The requested Amazon Resource Name (ARN) does not refer to an existing resource.
  //
  //   * ErrCodeInvalidStateException "InvalidStateException"
  //   The private CA is in a state during which a report or certificate cannot
  //   be generated.
  //
  //   * ErrCodeInvalidTagException "InvalidTagException"
  //   The tag associated with the CA is not valid. The invalid argument is contained
  //   in the message field.
  //
  // See also, https://docs.aws.amazon.com/goto/WebAPI/acm-pca-2017-08-22/UntagCertificateAuthority