sapcc helm repo cannot be added because of certificate signed by unknown authority

[Ninsbean]

Somehow I cannot add the helm repo to my helm list. It says that the certificate is not verified.

$ helm repo add sapcc https://charts.global.cloud.sap
Error: looks like "https://charts.global.cloud.sap" is not a valid chart repository or cannot be reached: Get "https://charts.global.cloud.sap/index.yaml": x509: certificate signed by unknown authority

I tried to skip TLS verify but it says it's "AuthorizedOnly"

$ helm repo add --insecure-skip-tls-verify sapcc https://charts.global.cloud.sap
Error: looks like "https://charts.global.cloud.sap" is not a valid chart repository or cannot be reached: failed to fetch https://charts.global.cloud.sap/index.yaml : 403 AuthorizedOnly

What can I do to add the helm repo?