Unfortunately there is an error in the english translation of the tutorial:
The line with "{ # # }" should be replaced with "{# #}". This line marks the start of the http body and is used for calculating the content length. With the additional space characters it is not recognized and the content length is wrong. The following template should work:

add=/tpl/j/cloud.tpl

Authorization: Bearer {{pushtab_var1}}
Content-Type: application/json; charset=utf-8
{# #}
{"{{sensortab_name.0}}": {"value": "{{sensortab_value.0}}", "unit":"{{sensortab_unit.0}}"}, "{{sensortab_name.1}}": {"value": "{{sensortab_value.1}}", "unit":"{{sensortab_unit.1}}"}}