JSON prase error: unexpected identifier "invalid"

What does this error mean? Someone just tried to mint, got this error and ended up accidentally minting 2 tokens.

Suspect a transient error. Can you share a link to this claim page?

Anyone has more info about this error?
Same happened to a collector that was trying to mint one of my editions from a chromebook
(and I did not set up the page for minting from mobile.
Might be that the cause?

this is the page that gave the problem: