From engagement letter to retainer to paid invoice, in one thread.
Accountants, consultants, agencies, bookkeepers and advisory firms bill on relationships, not transactions. The work starts with a document to sign, continues as a monthly retainer or a milestone invoice, and ends with a client who wants a clean record of everything they've paid. OptiPay360 handles all three without a separate eSign tool, a separate subscription biller, and a separate client portal.
How the day actually runs
- 1Engagement letter signed
Upload your existing PDF engagement letter or SOW, send it for signature, and get the executed copy back with a timestamped audit trail.
- 2Retainer set up
Create a recurring schedule on card or bank account for a monthly retainer, with automatic retries when a card expires.
- 3Project and milestone billing
Send itemized invoices for out-of-scope work or milestone draws, with payment terms and automatic reminders.
- 4Client self-serves
Clients sign in to the portal to pay, download past invoices, and update the payment method on file — instead of emailing your admin.
The parts of OptiPay360 you'll use most
Document signing (eSign)
Send any PDF — engagement letters, SOWs, NDAs — for signature with a full audit trail. Available on Business Elite.
Recurring retainers
Monthly or installment billing on a stored card or bank account, with retry logic when a payment fails.
ACH on large invoices
Bank transfer for five-figure invoices where card economics don't work, with the account securely tokenized.
Itemized invoicing
Line items, taxes, payment terms, deposits, and partial payments, with reminders that go out on their own.
Client portal
A branded portal where clients view every invoice and payment and manage their saved methods.
Penny, in-app assistant
Ask about a client's balance, draft a follow-up, or find an invoice without digging through screens.
What that adds up to
- Signature, retainer, and invoice history attached to one client record.
- Recurring revenue that keeps running when a card expires, instead of quietly stopping.
- ACH as a real option, not a workaround, on your largest invoices.
- Fewer 'can you resend that invoice' emails, because the client can get it themselves.