how to enable apple music 12 months subscription?

Hello

I've just bought apple music 12 months subscription gift card from paypal digital gifts ($99, via Ebay)

The redeem code claim link arrived through Email,

but when i redeemed it on my iPhone (6S) through the redeem button on the claim link,

and selecting the option 'redeem and use for 12months apple music subscription' on iTunes, the app didn't proceed.

(just white screen, as if the app was temporarily suspended under internet connection loss?)

After that, I opened the Music app to check my subscription status, only to find out that it was still 'individual (1 month)'.

Also, my apple ID has been credited with $99. I just don't know how to convert this to a 12months subscription.

I tried 'subscription management' on iTunes (on both iPhone and mac), with no avail.

Any help would be greatly appreciated!