Update Form

Change what a form collects — add a field, relabel one, tighten a rule, reorder, retire one — on a form that already exists. Composing the field itself is not here: About Form Fields (opens in a new tab) owns the identifier / inputType / componentType table and the options/enum shapes, and Create Form § Silent breakers apply to an added field exactly as to a created one.

A PATCH, never a delete-and-recreate. An update keeps the formId everything downstream already holds — a frontend binding, an automation, a saved dashboard view — and spends no slot against the site’s form cap.

The call

• ⚠️ namespace is a REQUIRED query parameter on the read, and this is what a revise run trips over. Without it the read returns 400 namespace has size 0, expected 10 or more, namespace must not be empty — a violation naming a field, so it reads like a body problem. Fix the call, don’t reshape the payload. (The filter on POST .../v4/forms/query needs it too.)
• The read-back is the body. Apply your change to what the GET returned and send that as form. namespace is immutable and travels along; there is no fieldMask, and no revision outside form — inventing either is a silent partial write.
• ⚠️ Append to formFields; never rebuild the entries you read. [...form.formFields, newField] works. Mapping the array to “clean up” each field — dropping fieldType, re-shaping an options block — fails with fieldType cannot be provided with any these fields: input_options, display_options on every field at once. The read-back’s field objects are already a valid write shape: pass them through untouched and touch only the one field you are changing.
• formFields is replaced wholesale. Wix: “Any field that’s missing from the array you send is moved to deletedFormFields, so resend every field you want to keep.” Same for steps[].layout — miss an item and that field goes unplaced, which renders empty. Drops are recoverable from deletedFormFields, but nothing announces them.
• A stale revision is rejected — re-GET and re-apply; never guess or increment it.
• Plan caps apply to an added field. Field count reached its limit of N on a PATCH is the site’s premium cap: reduce or upgrade, with the choice put to the user (Create Form § Plan caps). Never split the form across schemas to dodge it.

Adding a field

Start by reading About Form Fields (opens in a new tab) § Field types and § Choice fields for the field kind you’re adding: it gives the identifier / inputType / componentType triple — take all three from one row, and note that a dropdown or radio is inputType: "STRING" — plus the options/enum shape and the GUID every option needs. Create Form § Choice fields carries a complete dropdown body to copy. Composing a field from memory is what turns one PATCH into eight.

Then four things are yours to generate:

• id — a fresh lowercase GUID (uuidgen | tr 'A-Z' 'a-z'), unique in the form.
• target — the immutable submission key, unique across the form: snake_case plus a short random suffix (job_industry_7f2b). A duplicate target is accepted and silently stores nothing for every field but one.
• one GUID per choice option — options[] each need their own, exactly like the field’s; a readable slug is rejected (Create Form § Choice fields). Generate them with uuidgen, never by hand.
• the choices, declared twice — every option needs id + value + label, and validation.enum must list every one of those values. An empty validation is a free-text field, not a dropdown; the general “always include validation, even as {}“ rule does not apply here, and getting it wrong is accepted with a 200.
• the layout item — append to steps[<n>].layout.large.items, mirroring into medium / small if the form has them:

A field missing from the layout isn’t dropped, but it sorts last and has no defined position in the owner’s builder. To place it mid-form, insert at that row and bump every item at or after it — row restarts at 0 in each step.

A choice field’s identifier is its kind — DROPDOWN, RADIO_GROUP, CHECKBOX_GROUP, TAGS — never TEXT_INPUT, which is accepted and stored as a plain text input (Create Form § Choice fields).

The other changes

Verify — an update regresses a form exactly as a create can

A 200 on the PATCH proves the body parsed, nothing about what was stored. Read the form back, every time:

Assert on that read-back, not on the PATCH response:

• the changed field is there, carrying the identifier and componentType you sent — a choice field with a non-empty options[], which is where a dropdown that degraded to a text input shows up;
• every field you meant to keep is still present, and every inputOptions.required still reads back as sent;
• formSummary.fields still holds one entry per input field — that is what the owner’s dashboard renders.

Then hand back the dashboard links (Forms Dashboard Navigation): the form builder at wix-forms/form/{formId}, and that form’s submissions at wix-forms/form/{formId}/submissions. New submissions carry the new field; past ones don’t.

Troubleshooting

Related Documentation

• Create Form — composing fields, the identifier table, choice fields, the layout rules, plan caps
• Forms Dashboard Navigation — the builder and submissions links to hand back
• Update Form (opens in a new tab) — the PATCH contract and its replace semantics
• Form object (opens in a new tab) — revision, hidden, deletedFormFields, steps[].layout
• About Form Fields (opens in a new tab) — every field-level rule