I am a newbie with RESTful APIs and have never tried accessing one from inside Mathematica. I am trying to access the Companies House API, in the UK. The following command works fine from the Terminal command line (company number 00000006 is just a number a picked at random):

curl -X GET -u My_API_Key: https://api.companieshouse.gov.uk/company/{00000006}

I entered the following code in a Mathematica notebook, following the help example:

urlRoot = "https://api.companieshouse.gov.uk/company/";
company = "{00000006}";
myKey = "My_API_Key";
requestURI = URLBuild[{urlRoot, myKey, company}]

with my actual key in place of My_API_Key. The URI created is this:

https://api.companieshouse.gov.uk/company/My_API_Key/%7B00000006%7D

When I execute this command:

response = URLExecute[requestURI, "RawJSON"]

I get the dialog into which I enter My_API_Key and some blank spaces for the password. That's because the API documentation says to do this, or at least this is what I have understood. The result is this:

<|"error" -> "Empty Authorization header", "type" -> "ch:service"|>

What am I doing wrong? Very sorry if this is a really simple/dumb question, I have never tried doing this before... Thanks