Create naming series based on POS abbr like company wise

I tried adding abbr field in POS profile form as I need auto naming series in a custom form. As the client has a POS and a booking system within all the shops the booking system best lies in the POS app. I need the booking ID to have differed abbr of different POS based on the user logged in.
So user A of Shop A will get EC-xxxxx ID auto generated
So user B of Shop B will get PE-xxxxx ID auto generated
The abbr field didn’t appear in the POS profile so any help would be highly appreciated.
Many thanks in advance

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