Unrestricted Model API returns OAuth error

Client: Bayer Crop Science/Science at Scale

Issue: Our process calls a Model API (R) with unrestricted access using CURL. When we manually run it, we observe no issue; however, automation returns below error since July 14, 2021.

Missing OAuth provider. The service may not have been assigned a provider.

What condition in an unrestricted Model API can give this error?