I want to configure success message(successMessageTextBox) and downloadLink(linkTextbox) at form level(meta-data) through f
I would rather add this to the fr-form-metadata instance, e.g. by editing the source of the form in Form Builder, and adding, say, a <success-message> inside <metadata>:
<xf:instance xxf:readonly="true" id="fr-form-metadata" xxf:exclude-result-prefixes="#all">
<metadata>
...
<success-message>Submitted, all good!</success-message>
</metadata>
</xf:instance>
Then, in your process, you can show that message with:
success-message(message = "{xxf:instance('fr-form-metadata')/success-message}")