Why don’t my purchases get approved by the time I purchase it? It takes like 2 or more days to get charged on my card

It is approved at the time of purchase; if it wasn't approved, it wouldn't go through. Charges are then "pending" until reconciled. That process can take 1-2 days for any card purchase.

Whenever I try to make a purchase it doesn’t get approved and says there was an error

You are still charged instantly, not 1-2 days later. That's just when the transaction settles.