itemPosition: The position of the item on the form, including the sub-question position in the case of Matrix items. Alternatively, the item's id can also be used, as shown on the item's edit settings page or at the "Form Settings->Integrations->API" page, using the format idX=value.
YourValue: The URL encoded value with which to populate the given item
You can edit the link to include the items and values you wish to use. For text-based items like Short Answer fields, the value should be the text you want to display. For multiple-choice-based items like Radio Buttons and Checkboxes, the value should be the position of the choice, or choices, you want selected. Please note that all values should be URL encoded to prevent issues with special characters, and each Name-Value pair in the link should be separated with "&", as shown below.
Note: For multi-page forms, only items on the first page of the form can be pre-populated.
Note: Pre-populate does not work with Save & Return.
Pre-populate form link example
Following is an example of the Pre-populate form link for a form with Short Answer, Radio Button, Checkbox, Dropdown, Radio Button Matrix, and Checkbox Matrix items.
This form could be pre-populated as shown using a link like:
"id21=First+Lastname" corresponds to the item whose "id" is "21", and it will be pre-populated with the text "First Lastname". In this example, this could take the place of "2=First+Lastname" above, assuming the Short Answer's id is "21". You can find the ids for your form items at the "Form Settings->Integrations->API" page or in the Form Editor at the bottom of each item's edit window. It can be helpful to use the item ids rather than their position since the ids will not change if you add or move items.
As shown in the example below, you can combine these two approaches into a Pre-populate form link where you can use id for a form item and display position for another.