Ok. If you have a Firefly premium plan or Creative Cloud Pro (available in North America only), credits are only deducted for premium services. Nonpremium services do not result in credits being deducted. Since you have 4,000 credits, it seems likely that you have a Creative Cloud Pro plan (although there are other combinations of services that can result in 4,000 credits per month). This is documented in Generative credits FAQ:

The buy button allows you to buy more credits if needed. You can i
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