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Use an admin-scoped API key for these endpoints. Agent-scoped keys receive 403. You can also manage billing in the Inkbox Console.

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Check custom signature availability

Use the top-level mail_custom_signatures_enabled boolean in the subscription response to check whether your organization can configure automatic custom email signatures. This reports feature availability, not an individual mailbox’s on/off preference. Paid subscription details also include entitlements.mail_custom_signatures_enabled; entitlements may be null, so use the top-level field for this check.
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Configure content and the mailbox toggle through Update mailbox. Disabling or clearing a saved signature remains available even when this feature flag is false.

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Read current usage

Returns usage for your organization’s current billing cycle. Included SMS/MMS and call-minute allowances, and the listed overage rates, cover U.S. and Canadian numbers. International texting and calling use international lines with pricing by country. See Plans and pricing, or contact us to arrange an international line.
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Response (200)

Each entry in channels contains: Each entry in identities contains nullable identity_id, handle, and display_name, plus a channels array of event_type, count, and own_campaign_count. Its nullable sms_used, sms_limit, voice_sec_used, and voice_sec_limit fields report usage and allowances. A null identity ID represents unattributed usage.

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Read billing settings

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Response (200)

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Update billing settings

Omitted fields stay unchanged. The response returns both current settings. This example sets a $25 overage limit:
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When estimated overage spending reaches the limit, new sends and calls that would incur overage return 402 until the cycle resets or you raise the limit. Included usage remains available. Inbound and in-progress usage can exceed the limit, so this setting is not a strict invoice ceiling. Setting remove_branding_footer to true on the Free plan returns 403. The footer always appears on Free, even if you enabled its removal while on a paid plan. Custom email signatures are a separate paid-plan feature. Set signature_enabled on an individual mailbox to control its custom signature. Set remove_branding_footer here to control the organization’s Sent via Inkbox footer. Neither setting changes the other. When both appear, the custom signature comes first.