You are asking people if they want to use curve cash before use of a specific card on curve ( that’s right isn’t it) ?
Heres one for curve likes to be all modern how about helping people save instead of spending, ie spend to save.
Its a simple thing you join forces with a savings account of say 1.5% and give customer choice to save curve cash during the length of that card.
After this they either take it out or reinvest it if they reinvest internally in curves saving scheme then that should be either a ISA or a account where cant touch again but can’t add neither but interest is set higher/ but the customer starts again from zero with a new card to save again the only time you can add to the higher interest is through a large deposit or the end of curve card curve cash.
Hope this makes sense