Java

OkHttpClient client = new OkHttpClient();
        MediaType mediaType = MediaType.parse("application/json");
        String content = "{\n" +
                "    //populate email body\n" +
                "    \"bodyText\": \"Example Email with Link\\n\\nDear [Name],\\n\\nWe are pleased to inform you that you have been selected for the [Position] role at [Company Name]. Your skills and experience make you an excellent fit for the position, and we look forward to having you join our team.\\n\\nPlease click the following link to confirm your acceptance of the offer:\\n\\nAccept Offer (https://example.com/accept_offer)\\n\\nIf you have any questions or concerns, please do not hesitate to contact us at [email protected].\\n\\nBest regards,\\n\\n[Your Name]\\n[Company Name]\",\n" +
                "    \"from\": {\n" +
                "        \"email\": \"SENDER_EMAIL\",\n" +
                "        \"name\": \"SENDER_NAME\"\n" +
                "    },\n" +
                "    \"subject\": \"Example email with Java\",\n" +
                "\n" +
                "    //populate email recipient\n" +
                "    \"to\": [\n" +
                "        {\n" +
                "            \"email\": \"RECIPIENT_EMAIL\",\n" +
                "            \"name\": \"RECIPIENT_NAME\"\n" +
                "        }\n" +
                "    ],\n" +
                "    \"replyTo\": [\n" +
                "        {\n" +
                "            \"email\": \"RECIPIENT_EMAIL\",\n" +
                "            \"name\": \"RECIPIENT_NAME\"\n" +
                "        }\n" +
                "    ],\n" +
                "    \"cc\": [\n" +
                "        {\n" +
                "            \"email\": \"RECIPIENT_EMAIL\",\n" +
                "            \"name\": \"RECIPIENT_NAME\"\n" +
                "        }\n" +
                "    ],\n" +
                "    \"bcc\": [\n" +
                "        {\n" +
                "            \"email\": \"RECIPIENT_EMAIL\",\n" +
                "            \"name\": \"RECIPIENT_NAME\"\n" +
                "        }\n" +
                "    ],\n" +
                "    \"headers\": [\n" +
                "        {\n" +
                "            \"name\": \"HEADERS_NAME\",\n" +
                "            \"value\": \"HEADERS_VALUE\"\n" +
                "        }\n" +
                "    ],\n" +
                "    \"attachments\": [\n" +
                "        {\n" +
                "            \"mimeType\": \"image/png\",\n" +
                "            \"filename\": \"FILE_NAME.png\",\n" +
                "            \"value\": \"BASE64_ENCODED_CONTENT\"\n" +
                "        }\n" +
                "    ],\n" +
               "    \"metadata\": {\n" +
                "            \"key1\": \"METADATA_KEY1\",\n" +
                "            \"key2\": \"METADATA_KEY2\"\n" +
                "    }\n" +
                "}";

        RequestBody body = RequestBody.create(mediaType, content);
        Request request = new Request.Builder()
                .url("https://transmission.mailtarget.co/v1/layang/transmissions")
                .method("POST", body)
                .addHeader("accept", "application/json")
                .addHeader("Content-Type", "application/json")
                .addHeader("Authorization", "Bearer API_KEY")
                .build();
        Response response = client.newCall(request).execute();
    }