You need to make sure the Less IPs are whitelisted in the environment your OData endpoint is hosted in. You can find the IPs here.
Setup
There are two parts to setting up an OData source.Authentication
Authentication
Start by selecting basic or NTLM (Microsoft method) authentication. Then input the username and password.
Tables
Tables
In the next tab, you can input pairs of table names and URLs. The URL is the endpoint of the OData service while the table name is the name that will be used to identify the table in Less.You can add as many table pairs as you want - just click the ”+ Add table URL” button.