It should just be a simple authentication with your LOINC username and password. As you are posting to the forum, I assume you are able to log in to loinc.org so surely it’s not a password error. I’d suggest trying a cURL command to issue an authenticated request. It will prompt for a password.
curl -X GET -u myloincusername 'https://fhir.loinc.org/CodeSystem/$lookup?system=http://loinc.org&code=4544-3' --header 'Content-Type:application/fhir+json'
Please let us know whether or not you are able to get it work.
I apologize for the problems. I am unable to reproduce this error. I have tried with a number existing accounts and created a new one specifically to test. All worked successfully with the previous curl command.
Can I have your permission to change the password on your CragVFX account so I may test it directly? (You can update it thereafter, of course.) We did recently change our authentication storage so there’s a chance there could be something amiss with your account.
I was able to get that cURL command to work with your username and a new password. I tried from multiple hosts. I’m going to email you the new password so you may try yourself. After your testing, I suggest changing your password via http://loinc.org/forgot