If you want to leave "ACCPAY-" as part of the Ticket Number, you can do as Emre suggests, and I think the Ticket Number field in other tables in the DB is actually a character field rather than an integer anyway, so it shouldn't hurt to change that to a varchar in the table declaration as Emre shows.
If you want to strip out the characters, you can use SQL REPLACE, and even nest them if you have more than 1 prefix. Based on the screenshot shown by Emre, it would be this line:
,REPLACE(tkt.[TicketNumber],'ACCPAY- ','') as [TicketNo]
Multiple prefix replacements nested - it will start with the inner-most and work outward:
,REPLACE( REPLACE( REPLACE(tkt.[TicketNumber],'ACCPAY- ',''), 'AnotherPrefix',''), 'A3rdPrefix','') as [TicketNo]