Carriers see a failed check-in much the way they see fare evasion, which is why it does not go through the self-service correction that handles a forgotten tap-out. What actually produces a reversal is timestamped evidence, gathered while it is still there to gather.
This one's a failed check-in rather than a missed check-out, so it skips the usual self-service correction flow that handles a forgotten tap-out — you need to contact the specific carrier whose gate or reader failed on you, whether that's NS, GVB, RET, HTM or a regional operator, through their customer service channel. Bring proof: a screenshot of your OVpay app trip history showing the gap, or a bank statement showing the charge that resulted, with timestamps that back up your story rather than just a description of what happened. Carriers are generally reasonable about this once they see genuine payment-system evidence, since it's a known failure mode on their end, not yours. Keep a photo of the gate display too if you can grab one in the moment — it's the fastest way to get a reversal without a drawn-out back-and-forth.