Glissa Sunseeker — ruling 1

The artifact's mana value must be exactly equal to the amount of unspent mana you have when the ability resolves. If there's less mana or more mana, the artifact won't be destroyed.

Glissa Sunseeker — ruling 2

You need to have the unspent mana before the ability resolves. The ability doesn't allow you to activate mana abilities while it's resolving.

Glissa Sunseeker : règles, fonctionnement et interactions (MTG)

Glissa Sunseeker is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

First strike : Destroy target artifact if its mana value is equal to the amount of unspent mana you have.

How it works : Glissa Sunseeker

Original English text — Wizards of the Coast / Scryfall

#1December 1, 2004· Wizards of the Coast
The artifact's mana value must be exactly equal to the amount of unspent mana you have when the ability resolves. If there's less mana or more mana, the artifact won't be destroyed.
No other card is named in this ruling.
#2December 1, 2004· Wizards of the Coast
You need to have the unspent mana before the ability resolves. The ability doesn't allow you to activate mana abilities while it's resolving.
No other card is named in this ruling.