Dimming light with IFTTT and JSON

Hello All,

I am new here with a specific reason. the last 8 month I am trying to gain some more knowledge and experience with Domotica. As a full licensed HAM radioamateur I am always very interested in electronics. I modified some Sonoff modules and fuzzeled around with the well known ESP8266 boards. Although software or programming is absolutely now my strongest area, but I succeeded most of the time to get things running. So what is my problem?..

I bought a light dimmer (Armtronix) on Tindie which I want to control using Google Assistant, IFTTT and a JSON HTML commandline. I made a Applet in IFTTT with Google Assistant as (IF), “Say a phrase with a number” then Webhook and add a JSON commandline which looks like this: http://: /json.htm?type=command&param=switchlight&idx=21&switchcmd=Set%20Level&level=#
(for security reasons I removed my WAN IP and portnumber). My problem is that the # that stands for a number that equals the number I am calling when talking to my Google home, does do nothing to my light. however is I make this applet and use “say a simple phrase” and define in the JSON commandline a specific number (e.g. 75) like this: http://:/json.htm?type=command&param=switchlight&idx=21&switchcmd=Set%20Level&level=75
the IFTTT applet works fine and dims the light to 75%

Can anyone tell me what am I doing wrong here? I want to call the number tht equals the dimming percentage.