Merge branch 'dev' into docker

artifactory/commands/transferfiles/transfer.go

@@ -695,7 +695,14 @@ func validateDataTransferPluginMinimumVersion(currentVersion string) error {
 func getAndValidateDataTransferPlugin(srcUpService *srcUserPluginService) error {
 	verifyResponse, err := srcUpService.verifyCompatibilityRequest()
 	if err != nil {
-		return err
+		errMsg := err.Error()
+		reason := ""
+		if strings.Contains(errMsg, "The execution name '") && strings.Contains(errMsg, "' could not be found") {
+			start := strings.Index(errMsg, "'")
+			missingApi := errMsg[start+1 : strings.Index(errMsg[start+1:], "'")+start+1]
+			reason = fmt.Sprintf(" This is because the '%s' API exposed by the plugin returns a '404 Not Found' response.", missingApi)
+		}
+		return fmt.Errorf("%s;\nIt looks like the 'data-transfer' user plugin isn't installed on the source instance.%s Please refer to the documentation available at https://www.jfrog.com/confluence/display/JFROG/Transfer+Artifactory+Configuration+and+Files+to+JFrog+Cloud for installation instructions", errMsg, reason)
 	}
 
 	err = validateDataTransferPluginMinimumVersion(verifyResponse.Version)