DocuSign template fields not prefilled via Make API call (envelope created, values ignored)

Hi everyone,
I’m building a Make.com scenario to create a DocuSign envelope from a template and automatically prefill fields in the document.

What works:

• The envelope gets created successfully (status: created)

• The recipient (“Kunde”) is set correctly (name + email are correct)

What doesn’t work:

• None of the DocuSign fields get prefilled (even a static test value like "Test123" doesn’t show up)

This is the JSON body I send in Make (DocuSign “Make an API Call”):

{
  "status": "created",
  "templateId": "XXX",
  "templateRoles": [
    {
      "roleName": "Kunde",
      "name": "{{4.Accountname[1]}}",
      "email": "{{7.ContactEmail}}"
    }
  ],
  "recipients": {
    "prefillTabs": {
      "textTabs": [
        { "tabLabel": "vorname_nachname", "value": "Test123" },
        { "tabLabel": "Straße", "value": "{{7.InstallationAddressStreet2__c}} {{7.InstallationAddressStreetNumber2__c}}" },
        { "tabLabel": "PLZ Ort", "value": "{{4.Postleitzahl[1]}}" },
        { "tabLabel": "Ansprechpartner", "value": "{{4.`VE Requested by`}}" },
        { "tabLabel": "VE-Summe", "value": "{{4.`€ Value / Schaden (estimated)`}}" },
        { "tabLabel": "ContactPerson", "value": "{{SF.OwnerName}}" },
        { "tabLabel": "DamageList", "value": "{{DamageListString}}" }
      ]
    }
  }
}

Question:
Why would DocuSign create the envelope correctly but ignore all prefillTabs.textTabs values?

Things I’m wondering:

• Do prefillTabs work when creating an envelope from a template (with templateRoles)?

• Do the field identifiers need to be dataLabel/tabId instead of tabLabel?

• Could the fields in the template be the wrong type (e.g., sender/prefill fields vs recipient fields) or created in the “new editor” in a way that the API can’t address?

Any ideas on what to check or what the correct structure should be would be appreciated.