How to get user id in custom button invoke url?

How to get user id in custom button invoke url?

Hi , how i can get the user id of currecnt logged in user so i can send it with lead info to extennal api

this is button name : test api external


http://click2call.crecentech.com/?userid=${Users.User Id}

in console I see this error

  2. VM664:1 Uncaught SyntaxError: Unexpected token < in JSON at position 0
  3.     at JSON.parse (<anonymous>)
  4.     at zcrm8_ea36c_.js?env=crm&jscors=true:1
  5.     at Object.success [as successfn] (zcrm3_b5b46_.js?env=crm&jscors=true:1)
  6.     at Object.pushPendingResponse (zcrm3_b5b46_.js?env=crm&jscors=true:1)
  7.     at Object.processResponse (zcrm3_b5b46_.js?env=crm&jscors=true:1)
  8.     at Object.success (zcrm3_b5b46_.js?env=crm&jscors=true:1)
  9.     at h (zcrm-libs_39f1a_.js?env=crm&jscors=true:1)
  10.     at Object.fireWith [as resolveWith] (zcrm-libs_39f1a_.js?env=crm&jscors=true:1)
  11.     at n (zcrm-libs_39f1a_.js?env=crm&jscors=true:1)
  12.     at XMLHttpRequest.<anonymous> (zcrm-libs_39f1a_.js?env=crm&jscors=true:1)