One page of companies for the topic.

Invalid request: missing email or domain, empty items, more than 10,000 items, or a malformed body.

Missing or invalid API credentials.

Payment required: your organization cannot be billed for this request, so it was refused and nothing was billed. error says why:

• payment_method_required: no card or bank account is on file. An organization owner or admin adds one in the dashboard under Billing, then retry.
• subscription_inactive: the subscription was canceled. Reactivate the plan in Billing.
• terms_acceptance_required: no agreement is on file. An owner or admin accepts the terms in the dashboard.
• account_suspended_inactive: the account was suspended for inactivity. An owner or admin accepts the current terms in the dashboard.
• budget_exceeded: the monthly budget set for your organization or project is reached. See Project budgets.

Retrying does not help until the cause is fixed. Previews and dry_run requests bill nothing, so they work without a payment method: payment_method_required, subscription_inactive and budget_exceeded never refuse them.

Too many requests: the platform cap refused the request, or it was rate limited.

A platform cap refusal has error set to platform_cap_exceeded. Accounts have a daily and a monthly usage limit per meter, and kind says what retrying can achieve:

• limit_reached: this request would take usage past the limit. The same request succeeds once the limit resets at resets_at, which Retry-After gives in seconds.
• request_too_large: this request alone is larger than the limit, so retrying cannot succeed. Make it smaller (fewer items, or a smaller page_size), or contact support to raise the limit.
• shut_off: usage is paused for this account. Contact support.

message says the same in a sentence you can show your users.

Any other 429 is rate limiting: wait for Retry-After when it is present, then retry.