Apollo integration doesn't use Clay credits, so your Clay credit balance won't affect it.
For Apollo errors, ensure your Clay API key is linked correctly. If you're getting "Invalid credentials" errors, copy your Clay API key and add it to your integration account under the Integrations section, then save and retry.
You can also use your own Apollo API key instead of Clay's - go to your enrichment panel, select Account > Add Account, and switch from Clay's default to your own Apollo API key.