Belvo employs basic authentication using your secret keys. Just use your secretId as the username and secretPassword as the password. For example:
curl \
-u b951f3a9-xxxx-xxxx-xxxx-731208b2005e:hcrfb#vyklxxxxxxxxxxx8#[email protected]_q7jy9mclq7hk2
https://sandbox.belvo.com/api/
For information on how to get your API keys, check out our Get Started in 5 Minutes DevPortal article.