I flew from Krabi to Jakarta with Scoot. I had to buy one extra luggage at the airport because I couldn't do it online. The airlines charged me $1,625 for one 23-kg luggage. I thought this is a mistake but at that time I had no choice so I paid.
I sent an email to their office and was told that is the correct amount. I bought extra luggage before from Jakarta to Toronto, and it cost me $250.
Scoot's fare chart is here: https://www.flyscoot.com/en/plan/scoot-fees-chart For one extra bag from Krabi to Jakarta this should have been around 6000 Thai Baht or $165.00 US, which seems off by a factor of 10.
Of course, this all depends on what the conditions of your original tickets are and what else you checked or services you bought. I suggest carefully reading the receipt which should list the individual charges (if its more than one) and what tarifs applied.
