I sometimes order rarer components to be reserved at JLCPCB so that they are available when I place a PCB SMT assembly order.  The problem is the amount I transfer is usually too much so there is a refund.  But this is made in US$ which automatically gets converted back to UK£ by the credit card company so there is a currency conversion charge both ways.  Would it not be possible for JLCPCB to hold this money on account in US$ for my next order ?  I'd happily keep say $100 with JLCPCB so as to avoid these constant micro-transactions.