You may not be able to update your phone number due to the following reasons:

1) You may have input an invalid phone number format (type in your number without the country code +60. e.g: If your mobile number is +60123456789, you would just need to enter 123456789)
2) There may already have been another ShopBack account registered under your phone number

If you have any further queries, please do not hesitate to click here and we will be glad to assist you!