Thanks for posting in the Community.
First we'd like to make sure you're not trying to activate a trial if you're not eligible for it. This link will activate a normal Premium subscription without a start trial: https://www.spotify.com/purchase/offer/premium/
Follow it in an incognito window and if possible on another browser/device.
If that doesn't work, could you try with another payment method? Here you can find more on how to pay for a subscription and also some troubleshooting tips for failed payments.
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