Custom fields not autofilling on iOS

So one of the features I love about Bitwarden that does not seem to exist on other password managers is that it can autofill custom fields on different sites. This works perfectly on browser+extension.

Using iOS+Safari, I went to a site that I had pre-programmed Bitwarden to populate its form, I chose Bitwarden to Autofill but iOS said that there are no “login” items for the site. Is this a Bitwarden limitation or iOS limitation?