Form sumbission blank screen after email submission

Hi all, I might be making a silly mistake here, but I made some updates to my Klaviyo mobile email capture and now whenever someone submits their email opt-in the next screen is blank (it should ask for their first name then go to the success screen). I’ve tried removing the name step and have the same issue with the blank screen after they select “reveal £10 off code”.

• Emails aren't flowing into my Klaviyo email list (so feels like an issue with Klaviyo submission)
• Looks fine within preview
• The background colour that's showing isn't what I've set (should be dark green), I've tried changing block colours to try identify what's causing it.
• Issue is persistent across Chrome & Safari
• Desktop seems to be working fine with same settings

I've tried rebuilding it from scratch and get the same issue. Any ideas? I'm pulling a blank and have had to disable my mobile email capture for now (not ideal).

Thanks!