Payment for Sundry Debt

I paid a fee on behalf of a client and journalled it (I hope correctly) to Sundry Debtors (1101).
This is not a Sale and I can just ask for the repayment and apply the funds when they come in, but I would like to issue an ‘invoice’ (separate or combined with my fees). Is that the right way and what do I do when they pay up?

Thanks

To keep thing simple, just do another journal when you get money for this fee you paid on behalf of the client and treat the invoice as usual

Thanks,
I like simple.