@Mansi Gusain I think the reason that URL refresh is not enabled for your source URL is because it detected the data in the URL as unstructured data. Unstructured is set to Yes for the URL you added, If you add a URL which has structured data like a FAQ document the button should be enabled and also the column for Unstructured will be No.
For example, I have added this link and it allows a refresh on the URL since it marks it as Unstructured No.
For the other query regarding the number of sources, I think there is no limit on the number of sources you could add as a KB. See this page for limits and boundaries of custom Q&A.
Custom question answering currently has no limits on the number of sources that can be added. Throughput is currently capped at 10 text records per second for both management APIs and prediction APIs. When using the F0 tier, upload is limited to 3 files.
I hope this helps!!
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