How does Alternate Supplier Work with Supplier Capacity Constraints?

Summary: How does Alternate Supplier Work with Supplier Capacity Constraints?

Content (required):

We have switched on the supplier capacity parameters and loaded ASLs and supplier capacities. We are using buy items only. We are expecting alternate suppliers to be used if a supplier capacity is exceeded but alternate suppliers are not being used.

Please can someone clarify how alternate supplier fucntionality works and how it works with supplier capacity in particular.

Version (include the version you are using, if applicable):

Code Snippet (add any code snippets that support your topic, if applicable):