You need a white-label, multi-tenant eSign API with per-document pricing and full sender control.

Top picks:

• Meon eSign API – Low-cost, per-doc, unlimited senders, SMS signing links, mobile hand-drawn signatures, full branding control.

• eSign Genie – Affordable, hand-drawn signatures, SMS, embedded signing, webhooks.

• SignRequest – White-label, mobile-friendly, SMS, PDF field mapping.

• HelloSign (Dropbox Sign) – Polished UI, API control, SMS extra cost.

  Recommendation: For cost + features, start with Meon or eSign Genie.