To shed some light on the issue.
If you are receiving a response from the backend that says It's not allowed to execute this call from the current channel, then you have misconfigured your storefront.
Basically, the endpoint is most likely hitting an endpoint used for B2B or B2C depending on which 'channel' you are currently in.
For example, in the screenshot, you are currently in B2C, but you are most likely calling the B2B channel. You should be calling the endpoint with users/${userId}/carts/${cartId}/entries?quantity=${quantity}, but instead, you are calling an endpoint with orgUsers/${userId}/carts/${cartId}/entries?quantity=${quantity}.
Notice users vs orgUsers as the difference.