Добавление переменной в строку

Нужно вставить переменную в переменную (Будут двойные кавычки в самом конце строки от параметров recaptchaResponseToken и channelId). Переменные string

var body = @"{""context"":{""client"":{""hl"":""ru"",""gl"":""RU"",""remoteHost"":""83.221.223.190"",""deviceMake"":"""",""deviceModel"":"""",""visitorData"":""CgszNnBrYkRyMTUtcyjHs5GVBg%3D%3D"",""userAgent"":""Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/102.0.0.0 Safari/537.36,gzip(gfe)"",""clientName"":""WEB"",""clientVersion"":""2.20220609.00.00"",""osName"":""Windows"",""osVersion"":""10.0"",""originalUrl"":""https://www.youtube.com/watch?v=Oyf0feE9Ewo"",""screenPixelDensity"":1,""platform"":""DESKTOP"",""clientFormFactor"":""UNKNOWN_FORM_FACTOR"",""configInfo"":{""appInstallData"":""CMezkZUGELfLrQUQ2JquBRCUj64FELiLrgUQrp6uBRCYh64FEJjqrQUQmN79EhDUg64FEIKOrgUQkfj8EhDYvq0F""},""screenDensityFloat"":1.25,""timeZone"":""Europe/Moscow"",""browserName"":""Chrome"",""browserVersion"":""102.0.0.0"",""screenWidthPoints"":886,""screenHeightPoints"":754,""utcOffsetMinutes"":180,""userInterfaceTheme"":""USER_INTERFACE_THEME_LIGHT"",""connectionType"":""CONN_CELLULAR_4G"",""memoryTotalKbytes"":""8000000"",""mainAppWebInfo"":{""graftUrl"":""https://www.youtube.com/c/MusicLabWork/about"",""pwaInstallabilityStatus"":""PWA_INSTALLABILITY_STATUS_CAN_BE_INSTALLED"",""webDisplayMode"":""WEB_DISPLAY_MODE_BROWSER"",""isWebNativeShareAvailable"":true}},""user"":{""lockedSafetyMode"":false},""request"":{""useSsl"":true,""internalExperimentFlags"":[],""consistencyTokenJars"":[]},""clickTracking"":{""clickTrackingParams"":""CCJ0t2EpfgCFcU7mwod5WkExA==""},""adSignalsInfo"":{""params"":[{""key"":""dt"",""value"":""1654938056328""},{""key"":""flash"",""value"":""0""},{""key"":""frm"",""value"":""0""},{""key"":""u_tz"",""value"":""180""},{""key"":""u_his"",""value"":""5""},{""key"":""u_h"",""value"":""864""},{""key"":""u_w"",""value"":""1536""},{""key"":""u_ah"",""value"":""824""},{""key"":""u_aw"",""value"":""1536""},{""key"":""u_cd"",""value"":""24""},{""key"":""bc"",""value"":""31""},{""key"":""bih"",""value"":""754""},{""key"":""biw"",""value"":""870""},{""key"":""brdim"",""value"":""0,0,0,0,1536,0,1536,824,886,754""},{""key"":""vis"",""value"":""1""},{""key"":""wgl"",""value"":""true""},{""key"":""ca_type"",""value"":""image""}],""bid"":""ANyPxKqh1o0fCfaE9JXKsulGKl1YwJt87cIFGt-6vXWVADoMYBJIcajngNTg""}},""recaptchaResponseToken"":"""",""channelId"":""""}";