Form Prefill not working

[Raakshasi]

Issue: You have noticed that the Form Pre-fill feature on your form fields is not working. You have also tested this is a normal browser as well as incognito browse by filling out the test form and then reloaded the landing page again expecting that reloading the landing page will show you a pre-filled form since you have submitted the form already.

Resolution :
Please confirm that you are reaching that page via a link sent in an email.
In April 2019 Form Prefill was updated per this document: https://nation.marketo.com/docs/DOC-6909-form-pre-fill-feature-upgrade
"What change is being made?
Starting April 24, 2019, Marketo will only pre-fill form fields if the URL used to navigate to the Marketo landing page contains a valid mkt_tok URL parameter value (which occurs when users click tracked links in Marketo emails). What that means is, any time a person is viewing a Marketo landing page with a form, the URL being used must contain the mkt_tok token in the query string, otherwise, the form on that landing page will not be pre-filled. If the URL in the browser window does have a valid mkt_tok tracking token, then the form within the page will pre-fill as expected with data corresponding to the person record associated with that mkt_tok."

[Chris_Wilcox · Accepted solution]

Shameless plug for @SanfordWhiteman 's pre-fill solution outlined on his blog. We use it, it's awesome. 

[Michael_Florin]

I recently noticed - and I guess I should have known all along - that lead.tokens on landing pages behave differently than form prefill. By that I mean that a {{lead.First Name}} token on a LP renders correctly, even if the person did not hit that LP from an email click-through. So obviously this token rendering works just through an existing cookie.

Now, that lead me to this silly idea for a form:

And that setting prefills the form just from munchkin. Does anybody do form prefill like this or does this have downsides I didn't think of?

[SanfordWhiteman]

It’s been tried and has major downsides.

First, Marketo doesn’t JSON-encode tokens. Therefore any value that requires encoding, including quotation marks and line breaks breaks the whole form (doesn’t just break the Pre-Fill — the entire form will not render).

Second, not all field types work with this method: see checkboxes and radios.

[SanfordWhiteman]

Also note my complete Pre-Fill solution (linked above) takes advantage of {{lead.tokens}} to do its magic. But it properly encodes them.