Unable to test a form on odk central

I have a form that is working on odk aggregate and using the xls file I have uploaded a draft on odk central with associated media files when I preview the definition am getting the following errors Request to https://mlw.mw/v1/test/yV4k79jB3J9x0OkZHa3Ow4BkGgLW1sNYabXC4kqX9bNAq0zWUnt44CuzsIUKdP7h/projects/2/forms/test/draft/formList?formID=simprints_verification_test failed." and "Unexpected token < in JSON at position 0"

Am using odk central version 1.1.1 first time to set up odk central and using postgresql.

Is this a form you previously used with ODK Collect? The web preview is provided by Enketo which may not support features that this form uses. I think that's especially likely seeing simprints in the formId. Please try making a draft submission with Collect (more in the docs).

Yes, the form works in ODK Collect when uploaded on Aggregate server. I tried removing some functions like pulldata and the simprints, still getting the same error

Could you attach that form?

Can you see previews or test forms for any other forms on your server?

As @Grzesiek2010 says, if other forms work, it would be helpful to see this specific form. If it's not sensitive, you can attach it to this post. If it is sensitive, you could direct message it to a member of the core team such as me or @Grzesiek2010. We would only use it to troubleshoot the error and then discard it.

Alternately, sharing the link to the draft page that shows the error message would be helpful. It should start with https://mlw.mw/-/. What I'd like to look at is whether there are any errors in the JavaScript console that could give us hints. You can also try this yourself -- on most browsers you can right click on the screen, select Inspect at the bottom of the menu and then find the Console tab.