Hi Viktoria,
I am using the similar way to get the issue resolved. However, I do it in an easier way.
As the page are viewed by both merchant and customers, therefore, I set up two separate pages with same content but different conditional filters:
Merchant - they can only see those records related to themselves and have the function to update redemption status.
Customers - they can see all those redemption records they have with all merchants
By doing so, there is no need to add any inline filter and merchant will only see their own related records.
By the way, there is another issue that I may need yr help, could you please have a look at this post? This one could be quite an interesting function that can further expand the imagination of using Softr built App. ➥ Is it possible to have a QR Code reader in Softr block? - #4 by twmeric
Feel free to exchange idea on it and see how this could be achieved in a lightest way. The mobile is so powerful, it is the matter how we can make use of its resources through webapp in a smarter way. Awaiting your comment and advice on it.