I've been invited to a wedding as a +1. Don't know the couple, only met groom once in passing. I have to travel really far to get there and take a day off work, so it's costing me. The invitation says something like "having you all there is the greatest gift we could wish for but if you want you can donate towards our honeymoon". I have no active desire to donate towards their honeymoon, as I am struggling to pay off debts and already spent over £200 on train tickets and accommodation. Is it completely socially unacceptable to not give a donation? I feel like people would think I was a dick if I didn't, and I'd feel resentful if I did and then couldn't pay my credit card bill.
Can I just give them a card? Am I overthinking things?