2569471 - URI does not specify a valid host name error occurs when checking the connection of a destination

When checking the connection of a destination in SAP BTP, you got error message "Backend is not available in the list of defined system mappings in Cloud connector". And you have confirmed hostname/port configured in the destination's URL parameter at SAP BTP Cockpit, and the hostname/port configured as Virtual Host in the SAP Cloud Connector are the same.

At the same time, you have an underline "_" in your hostname.
Another error that you encounter can be:

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Reason: URI does not specify a valid host name

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SAP BTP

SAP Cloud Connector, connection, destination, underscore, underline, period, minus, virtual hostname, port, ping, warning, r3, backend, on premise, on-premise, onpremise, name, naming, http, Catalog service is unavailable. Please try again, odata, BTP
, KBA , BC-CP-DEST , Destination service , BC-MID-SCC , SAP Cloud Connector On-Demand/On-Premise Connectivity , BC-NEO-CON , Neo to On-premise Connectivity service , Problem