Cloudflare is blocking a customer server

Hello,
A customer can’t access my auth0 domain in order to retrieve a token for M2M authentication.
When trying to do so they receive error 403 from cloudflare servers.
When they try to run the a cURL command from within their servers it pass so I’m assuming that some header that is automatically being added blocks them. How can I know what is the cause for the block?

Hi @nir.a,

Do you have more information about this? Could you please post the error and any additional details?

Thanks,
Dan