I need a little help

I put on a gift card with 100$ on it so I could get PlayStation Plus extra and when I tried getting it with the gift card and the rest of the money on the PlayStation it just says "An unidentified error has occurred. Try again in a few moments. Is PlayStation Network down or did I do something wrong https://100001.onl/?

I assume you need to redeem your gift card on the PlayStation store. The redeeming is done under the three period option on the PlayStation store menu if I remember correctly.

Once the code has been redeemed on the store, you can buy whatever you want, PS Plus.