is there better way

        when (info) {
            null -> {
                return unauthorized()
            }
            else -> {
                val validInfo = validator.validateInfo(info)
                when (validInfo) {
                    is Either.Right -> {
                        if (!validInfo.b.authorised) {

                            // authorised is false so return unauthorised
                            return unauthorized()
                        }
                        // authorised is true, so use the authorised token to create a certificate
                        val authorisedInfo = validInfo.b
                        val productService = productServiceBuilder.buildProductService(authorisedInfo)
                        // TODO add when (productService) here
                        //
                        return when (productService) {
                            is Either.Right -> {
                                val product = productService.b.getProduct(
                                        authorisedInfo.userId!!)

                                APIGatewayProxyResponseEvent()
                                        .withBody(jacksonObjectMapper().writeValueAsString(product))
                                        .withStatusCode(200)
                            }
                            is Either.Left -> {
                                systemError()
                            }
                        }
                    }
                    is Either.Left -> {
                        return systemError()
                    }
                }
            }
        }

what about:

(info ?: return unauthorized())
    .let(validator::validateInfo)
    .flatMap { validatedInfo ->
        val authorisedInfo = validatedInfo.takeIf { it.authorised } ?: return unauthorized()

        productServiceBuilder.buildProductService(authorisedInfo)
            .map { productService ->
                val product = productService.getProduct(authorisedInfo.userId!!)

                APIGatewayProxyResponseEvent()
                    .withBody(jacksonObjectMapper().writeValueAsString(product))
                    .withStatusCode(200)
            }
    }
    .getOrElse(::systemError)