OneLogin access token request not working (unauthorized) - credentials

Question

I just setup a OneLogin account and wish to do a basic test from the command line with curl according to the docs at
https://developers.onelogin.com/api-docs/1/getting-started/working-with-api-credentials
and
https://developers.onelogin.com/api-docs/1/oauth20-tokens/generate-tokens-2
I get "unauthorized" despite many permutations of the curl command. Let me start with the curl command as included in the docs in the second link above. I do this:
curl 'https://api.us.onelogin.com/auth/oauth2/v2/token' \
-X POST \
-H "Authorization: client_id:144a1200f765fc67f1e, client_secret:d2dc92524169ee2" \
-H "Content-Type: application/json" \
-d '{
"grant_type":"client_credentials"
}'
(fake client_id and client_secret is included so that you can see the form they take in my call, i.e., spaces, encoding, etc.)
Response:
{"status":{"error":true,"code":401,"type":"Unauthorized","message":"Authentication Failure"}}
So I tried everything I could think of in terms of the "Authorization" line. Here are some examples of what I tried:
# base64 encode just the client_id and the client_secret (i.e., separately encoded and independent)
Authorization: client_id:zODU1NjYwOTRiZjYwOWFiOWJiZDQ1NGZjNg==, client_secret:WIxY2NjZWJjNWJlZDJlZDdiYmFiMDZiYTkyNzY3M2IxZQ==
# result: unauthorized
# base64 encode "Basic <client_id:client_secret>"
Authorization: Basic NjllZTIxZGRjOWU5YjFjY2NlYmM1YmVkMmVkN2JiYWIwNmJhOTI3NjczYjFl
# result: unauthorized
# use Basic without base64 encoding id and secret
Authorization: Basic 094bf609ab9bbd454fc6:c5bed2ed7bbab06ba927673b1e
# result: unauthorized
And finally... here is an image of the credentials page to demonstrate that I indeed did create the id and secret in the proper place.

Answer 1

I'm embarrassed to give the solution to this answer and there is no way from the question anyone could have answered this correctly except by guessing.
I accidentally swapped the client_id and client_secret early in my work flow and never went back to double check them... or at least if I did double check them I made the same error twice.
My best guess for why I swapped them is that they appear in one order (client_id, client_secret) in the docs and API, and they appear in the reverse order in the OneLogin UI (client_secret, client_id). You can see this in my OP.
The correct curl command is the first one I gave in the answer... plain text client id and secret (not base64 encoded). Here it is again for reference:
curl 'https://api.us.onelogin.com/auth/oauth2/v2/token' \
-X POST \
-H "Authorization: client_id:bed2ed7bbab06ba927673b1e, client_secret:385566094bf609ab9bbd454fc6" \
-H "Content-Type: application/json" \
-d '{
"grant_type":"client_credentials"
}'