Adding New Matrix Block via Frontend in Craft 3

Question

Referencing https://craftcms.com/docs/3.x/matrix-fields.html#saving-matrix-fields I believe I did this correctly according to the docs and other posts here. My Matrix field is able to save edits, but when the field is empty adding a new block does NOT work.

POST data from the form submission:

Code:

{{ hiddenInput('fields[vendorLocations][blocks][new1][type]', 'address') }}
{{ hiddenInput('fields[vendorLocations][blocks][new1][enabled]', '1') }}
<select name="fields[vendorLocations][blocks][new1][fields][city]" required>
   <option value="">Choose One</option>
   {% for city in riCities() %}
     <option value="{{ city|title }}">{{ city|title }}</option>
   {% endfor %}
</select>

Desired CMS Result:

Answer 1

After talking to Craft Support (Thanks Oli!), the solution for Craft 3 is...

{{ hiddenInput('fields[vendorLocations][sortOrder][]', 'new:1') }}

{{ hiddenInput('fields[vendorLocations][blocks][new:1][type]', 'address') }}


<select name="fields[vendorLocations][blocks][new:1][fields][city]" required>
   <option value="">Choose One</option>
   {% for city in riCities() %}
     <option value="{{ city|title }}">{{ city|title }}</option>
   {% endfor %}
</select>

Make sure the proper entryTypeId, section etc. is defined for your form as well, this is just the specifics for the new matrix block.