In your Simple Inked you can create vouchers for time i.e. a voucher for 2 hours of time, which a client can purchase as a gift, or you can give this to them as a reward for times like when they refer a friend.
If the rates differ per artist, use a Variable Voucher feature—this means that you create the voucher as you go. Set the voucher amount to anything at all, make the calculation for the number of hours they're receiving, and create it on the fly in POS.
Creating a Variable Voucher for a client in POS.
Add the client to POS, click Add Items.
Choose Variable Voucher.
On the right side panel, fill out the details to create the voucher for your client.
Choose the operator who is giving/selling the voucher to the client in the Sold By menu, Retail Price is dependent on whether this voucher is one you are giving away for free, which means that the retail price is $0, but if you're creating this voucher to be available for clients to purchase as a gift, then the retail price is $300 (let's say that the hourly rate is $150, and it's for 2 hours), Gift Voucher Value is $300, choose the voucher expiry, and click Save.
The voucher is added to the clients sale, ready for purchase, or ready to give away as a reward. Click Receive Payment, choose the payment type (even if it's for $0 because you're giving it to them as a reward, just pick cash and it will go through as $0, and Finish Sale.
The next window to pop up will display the VOUCHER ID. It is important to write this unique VOUCHER ID on the physical voucher, which you hand to the client. This means that when the voucher comes back into the studio to be redeemed, you can track the voucher, along with it's remaining value and time left on it.
There you have it, creating Gift Vouchers on the fly in POS.